Process for the purification of graphite materials

Abstract

Provided herein is a process for purifying graphite, comprising electrochemically treating graphite containing impurities selected from metals, metal oxides, and combinations thereof in the presence of an electrolyte, whereby a portion of the impurities are removed as a result of the electrochemical treatment to provide purified graphite. Also provided are the purified graphite provided by such process, and anodes and batteries each comprising the purified graphite.

Description

[Technical Field]

[0001] The present invention relates to a process for purifying impure graphite. In particular, the present invention relates to a process for purifying impure graphite material by removing impurities such as metals, metal oxides, and combinations thereof. Properly purified graphite material has numerous uses, including carbon brushes, refractories, material composites, electrodes, lubricants, coatings, transportation, machine parts, textiles, and household consumer applications.

[0002] In its most preferred form, the present invention is specifically directed to a process for purifying graphite produced by the Hazer® process to produce iron-containing graphite having a particular selectable morphology, although it will be recognized that the present invention is not limited to this particular most preferred field of use.

[0003] Another aspect of the invention relates to purified graphite having reduced levels of metal and / or metal oxide impurities that can be produced by the process of the invention. [Background technology]

[0004] Carbon, or more specifically graphite, is considered to be an important material in the emerging green technology market, having been shown to be useful in energy storage, electrical conduction devices, catalyst supports, lubricant additives, and modern electronic devices.

[0005] Carbon has several different allotropes (i.e., different physical forms). Different carbon allotropes can have different physical properties. For example, diamond is the hardest naturally occurring substance, while graphite is extremely soft, breaks under very light pressure, and has a very low specific gravity. Diamond is transparent, can be the ultimate abrasive, and is an electrical insulator and thermal conductor, while graphite is opaque, a very good lubricant, and a good electrical conductor while being an effective thermal insulator. Carbon allotropes are not limited to diamond and graphite, but also include graphene (a two-dimensional crystalline carbon layer), amorphous carbon, glassy carbon, carbon nanofoam, and other allotropes of carbon that are particularly relevant to the Hazer® process, namely, carbon nanotubes (CNTs), carbon nano-onions (CNOs), and carbon microspheres (CMSs).

[0006] Graphite has numerous applications, including carbon brushes, refractories, material composites, electrodes, lubricants, coatings, transportation, machine components, textiles, and household consumption applications. Recently, specialty markets for graphite have emerged, including batteries for electric vehicles (EVs). As sales of EVs increase, demand for battery-grade graphite is expected to surge. Despite changes in battery chemistry, graphite is expected to remain a key component of EV batteries for at least the next decade. Both synthetic and natural graphite are used in lithium-ion battery anodes in the form of intermediate spherical graphite.

[0007] Certain applications may require very pure graphite. Furthermore, as will be appreciated by those skilled in the art, higher quality grades of graphite (i.e., pure) are useful for specialized applications such as those described above. High purity graphite (99.9%) can be 5-10 times more valuable than conventionally refined graphite (94%-98%).

[0008] The concept of refining graphite is not new. In fact, graphite beneficiation is widely practiced at the industrial level. There are two methods for obtaining a commercial concentrate or product: (1) flotation, which involves repeated re-grinding and flotation (up to seven times) to purify the concentrate, or (2) acid leaching (dissolving) the gangue with hydrofluoric acid (for silicate gangue) or hydrochloric acid (for carbonate gangue). Both methods rely on impurities being somewhat liberated or exposed from their inclusions in the graphite, limiting their applicability to graphite containing very small (nanometer-scale) impurities. Acid leaching is a hazardous and potentially polluting method. Furthermore, it will be recognized that the morphology of the refined graphite is destroyed by grinding and flotation.

[0009] U.S. Patent No. 2,787,528 discloses a process for purifying graphite to an ash content of less than 3%. U.S. Patent No. 2,787,528 discloses a process in which impure graphite is first treated with a dilute sulfuric acid solution and then with a weak caustic. The primary impurity in most high-carbon natural graphite is mica.

[0010] U.S. Patent No. 1,600,730 discloses a method for purifying and treating naturally occurring graphite from mines using an electrolytic cell to remove some of the natural impurities. The natural impurities in naturally occurring graphite extracted from schist geological formations, after mechanical refining, are silica, alumina, iron oxide, calcium oxide, magnesium oxide, sulfuric anhydride, and various alkalis. Notably, U.S. Patent No. 1,600,730 does not disclose the purity of the graphite after treatment with an electrolytic cell.

[0011] The Hazer® process has been shown to produce graphitic carbon with total graphitic carbon (TGC) values ​​of 70-97% w / w directly from the reactor. To appeal to high-end markets for graphite applications such as battery manufacturing, graphite purities of 99.9% or greater are required.

[0012] Table 1 below shows the prices of various graphite purities from 2013. As is readily apparent, increasing the purity of the graphite material increases the value of the product. [Table 1]

[0013] WO 2016 / 154666 describes the production of graphitic carbon by the Hazer® process. Along with graphitic carbon, the process also produces hydrogen. The feedstock is a hydrocarbon gas, most preferably a methane source, and the process involves contacting a low-grade iron oxide catalyst with the hydrocarbon gas at a temperature between 600°C and 1000°C to catalytically convert at least a portion of the hydrocarbon gas into hydrogen and graphitic carbon. The graphitic carbon deposits on the low-grade iron oxide catalyst, and the resulting graphite inevitably contains some iron-based contaminants.

[0014] WO 2017 / 031529 describes subsequent improvements to the Hazer® process that make it possible to selectively achieve graphite species of various morphologies. Because different morphologies of graphite exhibit different properties, commercial applications of graphite also depend heavily on the morphology. According to the process described in WO 2017 / 031529, four distinct morphologies of graphite can be selectively produced.

[0015] First, there are graphite fibers, which are fibrous carbon structures with lengths typically ranging from 100 nm to 100 microns; the best-known graphite fibers are carbon nanotubes (CNTs), which are cylindrical nanostructures containing single or multiple graphite sheets aligned concentrically or perpendicularly to a central axis.

[0016] Second, carbon nano-onions (CNOs) are structures consisting of multiple spherical graphite sheets layered concentrically from a central core, which are usually catalyst particles or voids; these carbon structures typically range in diameter from 50 to 500 nm.

[0017] Third, there are carbon microspheres (CMS), which are hollow spherical graphitic structures typically larger than 500 nm in size. They are spherical in shape and can also be chain-like. Naturally occurring CMS are found in meteorites.

[0018] Finally, the temperature and pressure parameters can be manipulated in the Hazer process to produce graphene characterized by a single layer or single digit layers of graphite sheets.

[0019] It will be appreciated that when using low grade iron oxide as a catalyst (most preferably in the form of Fe2O3, Fe3O4, hematite ore or goethite ore), as with previous iterations of the technology described in WO2016 / 154666, the graphite produced, regardless of morphology, may contain iron-based impurities at levels that require subsequent purification for its downstream applications in many emerging and established industries.

[0020] To date, Hazer graphite has been successfully purified to greater than 99.9% w / w using techniques including high temperature thermal purification and microwave-assisted acid digestion, however, these methods can be difficult to scale up and can be costly. Summary of the Invention [Problem to be solved by the invention]

[0021] It is an object of the present invention to overcome or ameliorate one or more of the disadvantages of the prior art, or at least to provide a useful alternative.

[0022] An object of preferred forms of the present invention is to provide a process capable of purifying graphite having high purity (i.e., greater than 90% or even greater than 99%).

[0023] It is an object of at least one preferred form of the present invention to provide a process that can purify graphite without affecting the morphology or degrading the graphite. [Means for solving the problem]

[0024] Although the present invention has been described with reference to specific embodiments, it will be recognized by those skilled in the art that the present invention may be embodied in many other forms.

[0025] The present invention generally relates to a process for increasing the purity of Hazer graphite to 50%-99.9% (by weight), preferably 80%-99.7%, by electrochemically extracting iron impurities. As an added benefit, it may be possible to recover the iron impurities as a high-purity catalyst for the Hazer® process. Experiments conducted by the inventors demonstrate that graphite in both solid and slurry forms can be purified by the electrochemical purification (ECP) process. However, the convenience associated with processing Hazer graphite as a slurry may come at the expense of reaction rate and / or power consumption. Results further demonstrate the purification of Hazer graphite on a gram scale and the potential for upscaling.

[0026] High purity graphite is used in numerous applications including carbon brushes, refractories, batteries, material composites, electrodes, lubricants, coatings, transportation, machine parts, textiles, and household consumer applications.

[0027] Chemical refining of naturally occurring mined graphite has been used to remove natural impurities from geological formations. However, regardless of the source (i.e., naturally occurring or synthetically produced graphite), achieving high purity graphite in an economically feasible manner has been difficult. However, some graphite samples (particularly those produced by the Hazer® process) have impurities highly encapsulated in the graphite material, making them more difficult to remove. Comminution is typically used to release the embedded impurities. However, in the case of nano-sized impurities (e.g., Hazer® process graphite), this is not always practical or possible. The technology proposed by the present invention provides a means to address this problem.

[0028] According to a first aspect, the present invention provides a process for purifying a graphite material, the process comprising: electrochemically treating a crude graphite material containing impurities selected from metals, metal oxides, and combinations thereof; Use of prescribed or regenerated electrolytes; spanning a prescribed period of time; Over a given voltage range; Over a given temperature range; using a predetermined anode composition; Using a Predetermined Cathode Composition whereby a portion of the impurities are removed as a result of the electrochemical treatment to provide a purified graphite material.

[0029] In embodiments, the process uses a predetermined permeable membrane that prevents contact of the graphite with the cathode, which could cause a short circuit.

[0030] In embodiments, the impurities are selected from metals, metal-containing impurities, non-metals, non-metal-containing impurities, organics, inorganics, and combinations thereof. In preferred embodiments, the impurities are non-carbon impurities. In particularly preferred embodiments, the impurities are metals. Most preferably, the metal is iron or iron-carbon species such as ferrite, austenite, and cementite.

[0031] In another embodiment, the crude graphite material is compressed prior to use in the process.

[0032] In another embodiment, the process does not involve stirring or agitation.

[0033] In another embodiment, the metal-containing impurities are selected from metal oxides, metal hydroxides, metal nitrates, carbonates, carboxylic acids, salts, and the like.

[0034] In embodiments, the refined graphite material has substantially the same morphology as the crude graphite material. Preferably, the graphite material has a morphology selected from graphite fibers (including carbon nanotubes), carbon nano-onions, and carbon microspheres.

[0035] In embodiments, the electrolyte is selected from metal or transition metal sulfates, sulfites (including bisulfates), phosphates, carbonates, bicarbonates, hydroxides, permanganates, chromates, dichromates, oxalates, formates, acetates, benzoates, halides, chlorites, perchlorites, and hypochlorites (e.g., perfluorates, hypobromites, etc.), acids, and mixtures thereof, such as sulfates and sulfuric acid. In particularly preferred embodiments, the electrolyte is ammonium sulfate, iron sulfate, or a mixture thereof. In another embodiment, the electrolyte is sulfuric acid or nitric acid. Preferably, the electrolyte is iron sulfate or ammonium sulfate. Those skilled in the art will recognize that any suitable salt can be used, so long as the selected salt(s) form soluble compounds and / or complexes with iron and / or metal impurities. In further embodiments, the electrolyte is selected from sulfides, phosphides, phenolates, superoxides, peroxides, oxides, silicates, sulfones, thiocyanates, thiosulfates, selenates, triiodides, azides, cyanides, cyanates, borates, fulminates, arsenates, vanadates, antimonates, and the like.

[0036] In embodiments, iron impurities precipitate on the cathode as iron dendrites. Typically, the iron dendrites are harvested and applied industrially. In some embodiments, the iron dendrites are used as catalysts in the thermocatalytic decomposition of methane to hydrogen and iron-contaminated graphite material. In other embodiments, the iron may be in the form of sludge. In certain embodiments, the sludge may be recovered, purified, and / or conditioned into a catalyst, e.g., a low-performance or high-performance catalyst, depending on post-processing methods. In a preferred embodiment, the sludge, once purified to produce an iron-containing catalyst, can be used in the Hazer process to produce hydrogen and graphite from hydrocarbons, preferably methane.

[0037] In embodiments, the iron impurities remain in solution. In embodiments, the iron impurities are precipitated from solution and used as a catalyst in the thermocatalytic decomposition of methane to hydrogen and iron-contaminated graphite material, for example, in the Hazer® process.

[0038] The precipitated iron can have a particular shape, size, and purity or composition (pure iron or complex). Precipitation can be accomplished as part of the cell or as a separate process.

[0039] In embodiments, the iron impurities are precipitated from solution and used as a catalyst in the thermocatalytic decomposition of methane to hydrogen and iron-contaminated graphite material. In embodiments, once precipitated, the iron impurities are dried, crushed, and / or filtered.

[0040] In an embodiment, the iron-contaminated graphite material is then purified by the process defined according to the first aspect of the present invention.

[0041] In embodiments, the process is carried out continuously, substantially continuously, or on a batch basis.

[0042] In certain embodiments, the process is carried out on a batch basis, with each batch containing between about 1 g and 3 kg of graphite material, for example, between about 1 g and about 10 g, or between about 10 g and about 20 g, or between about 20 g and about 30 g, or between about 30 g and about 40 g, or between about 40 g and about 50 g, or between about 50 g and about 60 g, or between about 60 g and about 70 g, or between about 70 g and about 80 g, or between about 80 g and about 90 g, or between about 90 g and about 100 g, or between about 100 g and about 200 g, or The batch may comprise about 200 g to about 300 g, or about 300 g to about 400 g, or about 400 g to about 500 g, or about 500 g to about 600 g, or about 600 g to about 700 g, or about 700 g to about 800 g, or about 800 g to about 900 g, or about 900 g to about 1 kg, or about 1 kg to about 2 kg, or about 2 kg to about 3 kg of graphite material. In embodiments, the process does not lose efficiency, or only minimally loses efficiency, with scale-up of the amount of graphite material in each batch.

[0043] In embodiments, the voltage range is between about 1 V and 300 V. Preferably, the voltage range is between about 5 V and 300 V. In certain embodiments, the voltage is about 20 V. A voltage of 20 V has been found to improve purification and enhance reaction kinetics over a 24-hour period compared to other voltage ranges. However, the final purity of the graphite material may not be increased.

[0044] In embodiments, the current is constant during the process. In other embodiments, the current is varied during the process. In certain embodiments, the current can be increased during the process to increase the reaction rate.

[0045] In one embodiment, the period is between about 30 minutes and about 2 weeks. In another embodiment, the period is between about 2 hours and about 96 hours. Preferably, the period is between about 24 hours and about 48 hours.

[0046] In an embodiment, the temperature range is between about 5°C and about 100°C. In an embodiment, the temperature range is between about 20°C and about 80°C. In an embodiment, the temperature range is between about 40°C and about 60°C.

[0047] In embodiments, the anode comprises one or more structures. Preferably, the structures comprise rods, plates, pieces, etc. In embodiments, the structures are crystalline or amorphous. In embodiments, the structures are graphitic. In embodiments, the structures comprise platinum or are platinum-coated titanium, preferably platinum. In embodiments, the anode comprises graphite, lead, lead alloy, platinum, platinum-coated titanium, and combinations thereof. In particularly preferred embodiments, the structures are platinum-coated titanium.

[0048] In embodiments, the cathode includes graphite, lead, lead alloys, platinum, platinum-coated titanium, and combinations thereof. In embodiments, the cathode includes platinum, platinum-coated titanium, and graphite electrodes, various grades of stainless steel, iron alloys, other transition metal alloys, etc. In a preferred embodiment, the cathode includes platinum-coated titanium.

[0049] In embodiments, the process further includes the use of a permeable membrane covering at least a portion of the anode, the cathode, or both. Preferably, the permeable membrane is a neutrally charged permeable membrane, an anion exchange membrane, or a cation exchange membrane. More preferably, the permeable membrane is selected from asbestos cloth, cellulose, glass cloth, filter cloth, glass cloth impregnated with silica gel, porous sintered stainless steel, vinyl chloride acrylonitrile, polysulfone, polyethersulfone (PES), polycarbonate, polytetrafluoroethylene, polyethylene terephthalate (PET), and combinations thereof. Alternatively, the membrane may comprise sintered metal and non-metallic materials, such as ceramics.

[0050] In an embodiment, the permeable membrane has a molecular weight cut-off (MWCO) of less than about 1 million Da. Preferably, the permeable membrane has a molecular weight cut-off (MWCO) of between about 10 kDa and about 0.5 kDa. More preferably, the permeable membrane has a molecular weight cut-off (MWCO) of about 3.5 kDa. In one embodiment, the permeable membrane has a flow rate of 0.1 to 100 L / min / dm@2 at 200 Pa. 2 Preferably, the permeable membrane has an air permeability of between 1 and 50 L / min / dm at 200 Pa. 2 More preferably, the permeable membrane has an air permeability of between 2 and 30 L / min / dm at 200 Pa. 2 It has air permeability between.

[0051] In embodiments, the purified graphite material has a purity of greater than about 95% w / w. Preferably, the purified graphite material has a purity of greater than about 99% w / w. More preferably, the purified graphite material has a purity of greater than about 99.5% w / w. Most preferably, the purified graphite material has a purity of greater than about 99.9% w / w.

[0052] In embodiments, the refined graphite material is used as the crude graphite material in the process to provide repeated refinement.

[0053] According to a second aspect of the present invention, there is provided a purified graphite material when purified by a process defined according to the first aspect of the present invention.

[0054] The present inventors have surprisingly discovered a novel and easy approach to purifying graphite at relatively low cost. The electrochemical process used (electrolytic cell or electrorefining) provides a surprisingly efficient and relatively low-cost process for the purification of graphite due to its simple operation.

[0055] In some embodiments, the impurities undergo a redox reaction during the electrochemical process that removes a portion of the impurities from the graphite. In some embodiments, the impurities that undergo a redox reaction during the electrochemical process form a salt, such as a metal salt. In some embodiments, the impurities that undergo a redox reaction during the electrochemical process form a water-soluble salt. In some embodiments, the impurities that undergo a redox reaction during the electrochemical process form a water-insoluble salt.

[0056] In some embodiments, the impurity is iron. The iron may be synthetic iron (e.g., from Fe3O4), naturally occurring iron (e.g., from hematite), elemental iron, or iron carbide. In some embodiments, the impurity that undergoes a redox reaction during the electrochemical process forms a cationic species. In some embodiments, the impurity that undergoes a redox reaction during the electrochemical process forms a cationic species. 3+ The formation of iron cation species such as

[0057] In some embodiments, the electrochemical treatment does not substantially affect or damage the morphology of the graphite. Advantageously, refining that does not damage or affect the morphology of the treated graphite can increase the yield and value of the purified graphite.

[0058] In some embodiments, the process involves the use of a permeable membrane between the cathode and anode during the electrochemical process, the membrane primarily serving to prevent the graphite from contacting the cathode and shorting out the electrochemical cell.

[0059] In some embodiments, the salt formed by the redox reaction further undergoes a salt metathesis reaction. In certain embodiments, the salt metathesis reaction forms an insoluble salt. In some embodiments, the insoluble salt formed by the salt metathesis reaction is iron hydroxide or an iron complex such as jarosite. Advantageously, insoluble salts such as iron hydroxide can be a valuable by-product formed during the purification process of the present invention. For example, iron hydroxide can be used as a catalyst for, for example, decomposing methane to form graphite and hydrogen gas (most conveniently via the Hazer® process). As will be recognized by those skilled in the art, various insoluble iron species can be used directly or indirectly as catalysts in the Hazer® process.

[0060] In some embodiments, the electrolyte is a sulfate. In some embodiments, the electrolyte is selected from the group consisting of ammonium sulfate, iron sulfate, sulfuric acid, and combinations thereof. Advantageously, when iron sulfate is used as the electrolyte, elemental iron forms on the cathode during the electrochemical treatment of impure graphite. The elemental iron can be in the form of dendrites, forming instead of insoluble iron hydroxide. However, those skilled in the art will understand that the cell can be adjusted (and may be preferred) so that the depositing metal does not form dendrites but instead forms a uniform metal coating around the cathode; dendrites are generally undesirable because they can cause short circuits. Similarly, elemental iron can be a valuable by-product formed during the purification process of the present invention. For example, iron can also be used as a catalyst for, for example, decomposing methane to form graphite and hydrogen gas (again, most conveniently by the Hazer® process).

[0061] In some embodiments, iron in solution is preferred, or instead of elemental iron being deposited on the cathode, elemental iron is precipitated as an insoluble species.

[0062] In some embodiments, the impurities are naturally occurring, e.g., natural impurities from geological formations such as mined graphite. In some embodiments, the impurities are synthetically occurring, e.g., impurities introduced as a result of synthetically producing graphite. For example, the process described in the above-referenced International Publication No. WO 2016 / 000115, which, along with International Publication No. WO 2017 / 031529, are incorporated herein by reference in their entirety.

[0063] In some embodiments, the purified graphite has a purity of greater than 90% (by weight), preferably greater than 95%, more preferably greater than 98%, and even more preferably greater than 99%. In some embodiments, the purified graphite has a purity of greater than about 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99%. In some embodiments, the purified graphite has a purity of greater than about 98.1, 98.2, 98.3, 98.4, 98.5, 98.6, 98.7, 98.8, 98.9, 99.0, 99.1, 99.2, 99.3, 99.4, 99.5, 99.6, 99.7, 99.8, or 99.9%. In some embodiments, the purified graphite has a purity of greater than about 99.95%.

[0064] According to another aspect, the present invention provides a process for purifying graphite, comprising electrochemically treating graphite containing impurities selected from iron, iron oxide, and combinations thereof, in the presence of an electrolyte comprising a sulfate, whereby a portion of the impurities are removed as a result of the electrochemical treatment to provide purified graphite.

[0065] According to a third aspect, the present invention provides purified graphite comprising impurities selected from metals, metal oxides, and combinations thereof, wherein the purified graphite has an impurity concentration of less than 20% w / w.

[0066] In some embodiments, the purified graphite has an impurity concentration of less than 15% w / w, preferably less than 10%, preferably less than 5%, more preferably less than 3%, more preferably less than 2%, and even more preferably less than 1%. In some embodiments, the purified graphite has an impurity concentration of less than 20%, 19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, or 1% w / w. In some embodiments, the purified graphite has an impurity concentration of less than 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, or 0.05% w / w.

[0067] According to a fourth aspect of the present invention, there is provided an anode material comprising a coating on a substrate, the coating comprising MnO (electrolytic manganese dioxide (EMD)), a carbon conductive additive in the form of a purified graphite material according to the second aspect, and a binder.

[0068] In some embodiments, the EMD is one or more of α-, β-, γ-, δ-, or λ-MnO 2 .

[0069] In some embodiments, the EMD consists essentially of α-, β-, γ-, δ-, or λ-MnO 2 , hi some embodiments, the EMD is γ-MnO 2 .

[0070] In some embodiments, the EMD, carbon conductive additive, and binder are mixed in a weight ratio of 4-9:2:1.

[0071] In some embodiments, the EMD, carbon conductive additive, and binder are mixed in a weight ratio of 7:0.1 to 3:1.

[0072] In some embodiments, the EMD, carbon conductive additive, and binder are mixed in a weight ratio of 7:2:0.1-3.

[0073] In some embodiments, the EMD, carbon conductive additive, and binder are mixed in a weight ratio of 4-9:0.1-3:0.1-3.

[0074] In one embodiment, the EMD, carbon conductive additive, and binder are mixed in a weight ratio of 7:2:1.

[0075] In some embodiments, the binder comprises a fluoropolymer selected from the group consisting of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP), perfluoroalkoxyl polymer (PFA), and polyvinyl fluoride (PVF).

[0076] In some embodiments, the binder is selected from the group consisting of carboxymethyl cellulose (CMC), sodium alginate, starch, styrene-butadiene rubber (SBR), xanthan gum, polyvinyl chloride (PVC), polyacrylic acid (PAA), polyvinyl alcohol (PVA), polyethylene glycol (PEG), and polyamide-imide (PAI).

[0077] In one embodiment, the binder comprises polyvinylidene fluoride (PVDF).

[0078] In some embodiments, the substrate comprises a metal foil.

[0079] In some embodiments, the metal foil is made of a conductive metal.

[0080] In some embodiments, the conductive metal is copper, zinc, aluminum, iron, or any mixture thereof.

[0081] In some embodiments, the coating at least partially surrounds the substrate.

[0082] In some embodiments, the coating surrounds the substrate.

[0083] In some embodiments, the coating has a thickness ranging from about 1 micron to about 25 microns.

[0084] In some embodiments, the coating has a thickness of about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24 or about 25 microns.

[0085] In some embodiments, the coating has a thickness ranging from about 5 microns to about 20 microns.

[0086] In some embodiments, the coating has a thickness ranging from about 7 microns to about 15 microns.

[0087] In one embodiment, the coating has a thickness of about 10 microns.

[0088] In some embodiments, the negative electrode has a -1 ~approx. 100Sm -1 The electrical conductivity is in the range of

[0089] In some embodiments, the negative electrode has a capacitance of about 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, or about 100 Sm -1 It has an electrical conductivity of

[0090] In some embodiments, the negative electrode has a -1 ~approx. 95mm -1 The electrical conductivity is in the range of

[0091] In one embodiment, the negative electrode has a -1 It has an electrical conductivity of

[0092] According to a fifth aspect of the present invention, A positive electrode and a negative electrode; An electrolyte in contact with the positive and negative electrodes wherein the negative electrode comprises a coating on a substrate, the coating comprising MnO (electrolytic manganese dioxide (EMD)), a carbon conductive additive in the form of a purified graphite material according to the second embodiment, and a binder.

[0093] In some embodiments, the EMD is one or more of α-, β-, γ-, δ-, or λ-MnO 2 .

[0094] In some embodiments, the EMD consists essentially of α-, β-, γ-, δ-, or λ-MnO 2 .

[0095] In some embodiments, the EMD is γ-MnO 2 .

[0096] In some embodiments, the EMD, carbon conductive additive, and binder are mixed in a weight ratio of 4-9:2:1.

[0097] In some embodiments, the EMD, carbon conductive additive, and binder are mixed in a weight ratio of 7:0.1 to 3:1.

[0098] In some embodiments, the EMD, carbon conductive additive, and binder are mixed in a weight ratio of 7:2:0.1-3.

[0099] In some embodiments, the EMD, carbon conductive additive, and binder are mixed in a weight ratio of 4-9:0.1-3:0.1-3.

[0100] In one embodiment, the EMD, carbon conductive additive, and binder are mixed in a weight ratio of 7:2:1.

[0101] In some embodiments, the binder comprises a fluoropolymer selected from the group consisting of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP), perfluoroalkoxyl polymer (PFA), and polyvinyl fluoride (PVF).

[0102] In some embodiments, the binder is selected from the group consisting of carboxymethyl cellulose (CMC), sodium alginate, starch, styrene-butadiene rubber (SBR), xanthan gum, polyvinyl chloride (PVC), polyacrylic acid (PAA), polyvinyl alcohol (PVA), polyethylene glycol (PEG), and polyamide-imide (PAI).

[0103] In one embodiment, the binder comprises polyvinylidene fluoride (PVDF).

[0104] In some embodiments, the substrate comprises a metal foil.

[0105] In some embodiments, the metal foil is made of a conductive metal.

[0106] In some embodiments, the conductive metal is copper, zinc, aluminum, iron, or any mixture thereof.

[0107] In some embodiments, the coating at least partially surrounds the substrate.

[0108] In some embodiments, the coating surrounds the substrate.

[0109] In some embodiments, the coating has a thickness ranging from about 1 micron to about 25 microns.

[0110] In some embodiments, the coating has a thickness of about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24 or about 25 microns.

[0111] In some embodiments, the coating has a thickness ranging from about 5 microns to about 20 microns.

[0112] In some embodiments, the coating has a thickness ranging from about 7 microns to about 15 microns.

[0113] In one embodiment, the coating has a thickness of about 10 microns.

[0114] In some embodiments, the negative electrode has a -1 ~approx. 100Sm -1 The electrical conductivity is in the range of

[0115] In some embodiments, the negative electrode has a capacitance of about 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, or about 100 Sm -1 It has an electrical conductivity of

[0116] In some embodiments, the negative electrode has a -1 ~approx. 95mm -1 The electrical conductivity is in the range of

[0117] In one embodiment, the negative electrode has a -1 It has an electrical conductivity of

[0118] In some embodiments, the electrolyte is an aqueous electrolyte.

[0119] In some embodiments, the electrolyte is an aqueous electrolyte present at a concentration in the range of about 0.01M to about 10M.

[0120] In some embodiments, the electrolyte is an aqueous electrolyte present at a concentration of about 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.95, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5 or about 10 M.

[0121] In some embodiments, the electrolyte is an aqueous electrolyte present at a concentration in the range of about 0.01M to about 5M.

[0122] In some embodiments, the electrolyte is an aqueous electrolyte present at a concentration in the range of about 0.01M to about 2M.

[0123] In some embodiments, the electrolyte is an aqueous electrolyte selected from the group consisting of sulfate salts, nitrate salts, chloride salts, and combinations thereof.

[0124] In some embodiments, the electrolyte is an aqueous electrolyte selected from the group consisting of ammonium sulfate, sodium sulfate, magnesium sulfate, iron sulfate, copper sulfate, zinc sulfate (ZnSO), cadmium nitrate, cobalt nitrate, sodium nitrate, sodium chloride, nickel chloride, potassium chloride, ammonium chloride, calcium chloride, sulfuric acid, and combinations thereof.

[0125] In some embodiments, the electrolyte is zinc sulfate (ZnSO), zinc chloride (ZnCl), ammonium chloride (NHCl), and zinc trifluoromethylsulfonate (Zn(CFSO)), or mixtures thereof.

[0126] In some embodiments, the electrolyte is an ionic liquid comprising a cation selected from the group consisting of 1-alkyl-3-methyl-imidazolium, N-alkyl-pyridinium, tetraalkyl-ammonium, tetraalkyl-phosphonium, and combinations thereof.

[0127] In some embodiments, the alkyl group is a C-C 12 alkyl.

[0128] In some embodiments, the ionic liquid comprises a cation selected from the group consisting of 1-ethyl-3-methyl-1H-imidazolium, 1-butyl-3-methyl-1H-imidazolium, 1-butylpyridinium, and combinations thereof.

[0129] In some embodiments, the electrolyte is ZnSO4.

[0130] In some embodiments, the ZnSO4 electrolyte is present at a concentration in the range of about 0.01M to about 10M.

[0131] In one embodiment, the ZnSO4 electrolyte is present at a concentration of 1.0M.

[0132] In some embodiments, the positive electrode is a zinc metal electrode.

[0133] In some embodiments, 0.05Ag -1 When measured between 1.5V and 0.7V at a current density of 1.5V, the negative electrode discharged approximately 50mAhg. -1 ~About 200mAhg -1 The specific discharge capacity is in the range between

[0134] In some embodiments, 0.05Ag -1 When measured between 1.5V and 0.7V at a current density of 1.5V, the negative electrode discharged approximately 70mAhg. -1 ~about 120mAhg -1 The specific discharge capacity is in the range between

[0135] In one embodiment, 0.05Ag -1 When measured between 1.5 V and 0.7 V at a current density of at least about 109 mAhg -1 It has a specific discharge capacity of

[0136] definition In describing and defining the present invention, the following terms will be used in accordance with the definitions set forth below. It will also be understood that the terminology used herein is for the purpose of describing particular embodiments of the present invention only, and is not intended to be limiting. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0137] The terms "graphite" and "graphitic material" are generally considered to be synonymous for the purposes of the present invention. This definition includes carbon materials that are crystalline (short-range and long-range crystalline), most preferably including the various morphologies described above in connection with Applicant's prior publication WO 2017 / 031529.

[0138] Unless the context clearly requires otherwise, throughout the description and claims, the words "comprise," "comprising," and the like, are to be construed in an inclusive sense, i.e., "including, but not limited to," rather than an exclusive or exhaustive sense.

[0139] As used herein, the phrase "consisting of" excludes any element, step, or ingredient not expressly specified in the claim. When the phrase "consisting of" (or variations thereof) appears within a clause in the body of a claim rather than immediately following the preamble, it limits only the elements specified in that clause; other elements are not excluded from the claim as a whole. As used herein, the phrase "consisting essentially of" limits the scope of a claim to the expressly specified elements or method steps and those that do not materially affect the basic and novel characteristics of the claimed subject matter.

[0140] With respect to the terms "comprising," "consisting of," and "consisting essentially of," when one of these three terms is used herein, the subject matter disclosed and claimed herein may include the use of either of the other two terms. Thus, in some embodiments not expressly stated otherwise, any instance of "comprising" can be replaced by "consisting of" or alternatively, "consisting essentially of."

[0141] Except in the working examples or where otherwise indicated, all numbers expressing quantities of ingredients or reaction conditions used herein should be understood to be modified in all instances by the term "about," taking into account ordinary tolerances in the art. The examples are not intended to limit the scope of the invention. Hereinafter, unless otherwise indicated, "%" means "% by weight" (or "% w / w"), "ratio" means "weight ratio," and "parts" means "parts by weight."

[0142] As used herein, the term "substantially" shall mean, where relevant, including more than 50% by weight, unless otherwise stated.

[0143] The recitation of numerical ranges using endpoints includes all numbers subsumed within that range (eg, 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.).

[0144] The terms "preferred" and "preferably" refer to embodiments of the invention that may offer certain benefits, under particular circumstances. However, other embodiments may be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the invention.

[0145] It should also be noted that as used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

[0146] The prior art owned by Hazer Group Limited referred to herein (i.e., WO 2016 / 000115 and WO 2017 / 031529) is hereby incorporated by reference in its entirety.

[0147] Any discussion of prior art throughout this specification should in no way be taken as an admission that such prior art is widely known or forms part of the common general knowledge in the field.

[0148] Although exemplary embodiments of the disclosed technology have been described in detail herein, it should be understood that other embodiments are contemplated. Accordingly, the disclosed technology is not intended to be limited in scope to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The disclosed technology is capable of other embodiments and of being practiced or carried out in various ways.

[0149] "Alkyl" as a group or part of a group, unless otherwise stated, refers to a linear or branched aliphatic hydrocarbon group, preferably C1-C 12 Alkyl, more preferably C1-C 10 It refers to alkyl, most preferably C1-C6 alkyl. Examples of suitable linear and branched C1-C6 alkyl substituents include methyl, ethyl, n-propyl, 2-propyl, n-butyl, sec-butyl, t-butyl, hexyl, etc. This group may be a terminal group or a bridging group.

[0150] "Aryl" as a group or part of a group refers to (i) an optionally substituted monocyclic or fused polycyclic aromatic carbocyclic ring (a ring structure in which the ring atoms are all carbon), preferably having 5 to 12 atoms per ring. Examples of aryl groups include phenyl, naphthyl, and the like; (ii) an optionally substituted partially saturated polycyclic aromatic carbocyclic moiety, including phenyl and one or more C 5~7 Cycloalkyl and / or C 5~7 It refers to cycloalkenyl groups (single or multiple) fused together to form a ring structure, such as tetrahydronaphthyl, indenyl, or indanyl. This group may be a terminal or bridging group. Typically, aryl groups are C6-C 18 It is an aryl group.

[0151] Throughout this specification, unless the context requires otherwise, the terms "synthetic," "synthetically derived," and the like will be understood to mean that the material has been synthesized by chemical techniques.

[0152] Throughout this specification, unless the context requires otherwise, the terms "natural," "naturally occurring," and the like will be understood to mean that the material has not been synthesized by chemical techniques, such as by mining from earth formations. The terms "natural," "naturally occurring," and the like include materials that occur in nature, but should not be understood to exclude materials that have undergone physical beneficiation, such as crushing, sieving, or sorting.

[0153] Selected preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0154] [Figure 1] 1A-1B are schematic embodiments of an electrochemical cell for purifying impure graphite, in particular, FIG. 1A is a 2D side view and FIG. 1B is a 3D schematic view showing spaced apart electrode plates.

[0155] [Figure 2] 1 illustrates an embodiment of the present invention in the form of a block diagram of an electrochemical refining plant.

[0156] [Figure 3] 1 is a flowsheet of an embodiment illustrating the configuration of an electrochemical refining plant.

[0157] [Figure 4] FIG. 1 shows a process flow diagram of an embodiment illustrating the configuration of an electrochemical refining plant.

[0158] [Figure 5] FIG. 5a is a photograph of the laboratory-scale electrochemical cell taken during testing, and FIG. 5b is a schematic diagram of the embodiment shown in the photograph of FIG. 5a at 3.5 kDa.

[0159] [Figure 6] 1 shows the thermogravimetric analysis (TGA) curves of electrochemically purified graphite after 24 hours of treatment.

[0160] [Figure 7] Photographs of the electrochemical purification of graphite for up to 48 hours are shown, showing that iron is removed from the graphite core in the form of Fe(OH) or iron complexes (e.g., day 1; 24 hour photographs).

[0161] [Figure 8] 1 shows the thermogravimetric analysis (TGA) curves of electrochemically purified graphite after 48 hours of treatment.

[0162] [Figure 9] Scanning electron microscope (SEM) images comparing crude and purified graphite samples are shown in Figure 9a, where Figure 9a shows the untreated graphite containing impurities before electrochemical treatment, and Figure 9b shows the electrochemically purified graphite.

[0163] [Figure 10] A backscattered SEM micrograph of the purified graphite after 48 hours of treatment is shown, with the graphite with the residual iron core retained circled.

[0164] [Figure 11] 1 is a photograph of elemental iron dendrites formed on the cathode instead of iron oxide when iron sulfate was used as the aqueous electrolyte.

[0165] [Figure 12a] Schematic of the ECP process for Hazer graphite slurry. This schematic shows an experiment in which a 16% v / v Hazer graphite / 1 M (NH4)2SO4 slurry was placed in a beaker and mixed with a magnetic stirrer. The dialysis bag contained 1 M (NH4)2SO4 and a carbon cathode. The experiment was carried out over a 24-hour period.

[0166] [Figure 12b]Graphite slurry testing is shown. Hazer graphite was mixed with electrolyte at 16% v / v to form a graphite slurry. The pure electrolyte was placed in a dialysis bag with the cathode, and the anode was placed in the slurry. Images show the process over a 24-hour period.

[0167] [Figure 13] This shows a TGA of red sludge collected from ECP purification. The thermal decomposition of the iron by-product in the TGA occurs in roughly four steps. These decompositions are similar to those seen in the literature and show 1) loss of water, 2) dehydroxylation resulting in loss of OH-, 3) loss of ammonia and water, and 4) loss of sulfuric acid from the ferrous sulfate. The ramp rate for the TGA was 15°C / min.

[0168] [Figure 14] A TGA-EG reactor system with 100% CH4 flow is used to demonstrate the catalytic performance of iron by-product (red sludge) at 900°C, 1 atmosphere and an 8 hour run.

[0169] [Figure 15] A comparison of TGAs of laboratory sample "PFBR-019-FL01" purified with different electrolytes. Each of the electrolytes used was able to purify the pilot plant graphite from about 80% to about 93%, but it is interesting to note that the pyrolysis of each sample was different, which may indicate a change in the graphite's structure.

[0170] [Figure 16] Figure 1 shows an FESEM image of the pristine graphite material before the ECP process.

[0171] [Figure 17] 17 shows an FESEM image of the purified graphite material from FIG. 16.

[0172] [Figure 18]Relative pressure and pore size for the pristine sample and purified graphite material. (a) N2 physisorption isotherms, and (b) pore size distributions for the pristine sample, samples from studies 1b, 3b, 4a, and 6.

[0173] [Figure 19] XRD patterns of the original sample and the treated graphite material are shown: (a) XRD pattern of the original sample (PFBR-26-FL01), (b) standard patterns of Fe (00-006-0696), C (01-089-8487), and FeC (01-089-7271), (c) and (d) comparison of XRD patterns of samples collected before and after ECP.

[0174] [Figure 20] Scanning electron microscope (SEM) images of the carbon materials used as conductive additives in this study: (a) Super P, (b) Carbon-O, (c) Carbon-T, and (d) Carbon-E.

[0175] [Figure 21] Particle size distribution profiles of the carbon materials used as conductive additives in this study: super P, Carbon-O, Carbon-T, and Carbon-E.

[0176] [Figure 22] (a) N2 physical adsorption isotherm, (b) pore size distribution, (c) Raman spectra, and (d) TGA profiles of different carbon materials: Super P, Carbon-O, Carbon-T, and Carbon-E.

[0177] [Figure 23] 1 shows the differential thermogravimetry (DT) profiles of different carbon materials: super P, Carbon-O, Carbon-T, and Carbon-E.

[0178] [Figure 24]Figure 1 shows the electrolyte absorption capacity over time of EMD electrodes fabricated with different carbon conductive additives.

[0179] [Figure 25] Galvanostatic discharge curves of Zn-C batteries fabricated with different carbon conductive additives at discharge current densities of (a) 1.0 Ag-1, (b) 0.5 Ag-1, (c) 0.1 Ag-1, and (d) 0.05 Ag-1. (e) Comparison of the specific capacity of Zn-C batteries at different discharge current densities. The inset shows an enlarged plot in the low discharge current density region. (f) Nyquist plot of the Zn-C battery. The inset shows the intercept of the impedance curve with the real axis.

[0180] [Figure 26] (a) GITT profiles of Zn-C batteries assembled with different carbon additives. (b) Enlargement of one GITT segment at the third test cycle. (c) Cell resistance of a Zn-C battery during 30 GITT test cycles. (d) OCV plot of a Zn-C battery during a one-month long-term stability test.

[0181] [Figure 27] Figure 1 shows the constant current discharge curve of a Zn-C battery under 0.1 Ag-1 after long-term stability testing. DETAILED DESCRIPTION OF THE INVENTION

[0182] Those skilled in the art will understand that the present invention includes the embodiments and features disclosed herein and all combinations and / or permutations of the disclosed embodiments and features.

[0183] process As noted above, one form of the present invention provides a process for purifying graphite material, the process comprising electrochemically treating a crude graphite material containing impurities in the form of metals; using a predetermined electrolyte; for a predetermined period of time; over a predetermined voltage range; over a predetermined temperature range; using a predetermined anode composition; and using a predetermined cathode composition, whereby a portion of the impurities are removed as a result of the electrochemical treatment to provide a purified graphite material.

[0184] In another form, the invention provides a process for purifying graphite, comprising electrochemically treating graphite containing impurities selected from iron, iron oxide, and combinations thereof, in the presence of an electrolyte comprising a sulfate or mixed composition, whereby a portion of the impurities are removed as a result of the electrochemical treatment to provide purified graphite.

[0185] The present inventors have surprisingly discovered a novel and easy approach to purifying graphite at relatively low cost. The electrochemical process used (electrolytic cell or electrorefining) provides a surprisingly efficient and relatively low-cost process for the purification of graphite due to its simple operation.

[0186] In some embodiments, the process steps of the present invention can be repeated. In certain embodiments, the process steps of the present invention can be repeated 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 (or more) times.

[0187] As will be appreciated by those skilled in the art, the impurities can be any applicable metal having dimensions in the nm to μm range. Suitable metals can be selected from the group consisting of alkali metals, alkaline earth metals, transition metals, rare earth elements, and combinations thereof. In certain embodiments, the metal is selected from gold, aluminum, copper, iron, lead, silver, platinum, tin, cobalt, nickel, zinc, and combinations thereof. In preferred embodiments, the metal is iron. In other embodiments, the metal is selected from titanium, sodium, potassium, magnesium, manganese, calcium, or phosphorus. In other embodiments, the impurities can include metalloids such as silicon or non-metals such as sulfur. It will be appreciated that there are many impurities that can be found in graphite, including any impurity that can be found in a typical iron-bearing ore.

[0188] Suitable metal oxides can be selected from the group consisting of oxides of alkali metals, alkaline earth metals, transition metals, rare earth elements, and combinations thereof. In certain embodiments, the metal oxide is aluminum oxide, copper oxide, iron oxide, silver oxide, tin oxide, cobalt oxide, nickel oxide, zinc oxide, and combinations thereof. In preferred embodiments, the metal oxide is iron oxide. In other embodiments, the oxide comprises silica.

[0189] In some embodiments, the impurities undergo a redox reaction during the electrochemical process, and a portion of the impurities are removed from the graphite. In preferred embodiments, the impurities are oxidized during the electrochemical process, and a portion of the impurities are removed from the graphite. In some embodiments, the impurities that undergo a redox reaction during the electrochemical process form a salt, such as a metal salt. In some embodiments, the impurities that undergo a redox reaction during the electrochemical process form a water-soluble salt. In some embodiments, the impurities that undergo a redox reaction during the electrochemical process form a water-insoluble salt.

[0190] In some embodiments, the impurities that undergo redox reactions during the electrochemical process form cationic species. In some embodiments, the cationic species are selected from gold cations, aluminum cations, copper cations, iron cations, lead cations, silver cations, platinum cations, tin cations, cobalt cations, nickel cations, zinc cations, and combinations thereof. In preferred embodiments, the impurities that undergo redox reactions during the electrochemical process are selected from Fe cations, aluminum cations, copper cations, iron cations, lead cations, silver cations, platinum cations, tin cations, cobalt cations, nickel cations, zinc cations, and combinations thereof. 2+ or Fe 3+ The formation of iron cation species such as

[0191] Without wishing to be bound by theory, it is believed that anions (preferably sulfate ions) of the electrolyte in solution undergo redox reactions with impurities as they are transported to the positive electrode (anode) during the electrochemical process, resulting in the impurities forming salts (i.e., metal salts). The metal salts (separated into cations and anions) that can dissolve in the solution can then diffuse out of the graphite, thereby removing the impurities from the graphite. The water-soluble metal salts can then react by salt metathesis to produce water-insoluble salts. Depending on the electrolyte used, elemental metals from the impurities may deposit on the cathode during the electrochemical process. For example, sulfate ions may diffuse into the graphite to form iron sulfate and then diffuse out as a dissolved salt, or iron impurities may undergo oxidation from Fe to Fe. 3+ which diffuses out of the graphite inclusions and then forms iron sulfate.

[0192] For example, if ammonium sulfate ((NH4)2SO4) is used as an electrolyte, the ammonium sulfate in water will dissolve according to the formula shown below, resulting in ammonium cations (NH4 + ) and sulfate anion (SO4 2- The negative sulfate ions are then electrostatically attracted to the positive electrode (anode, e.g., impure graphite), where the anions penetrate the graphite "core" to access the impurities. In the case of an iron core, the iron is converted by a redox reaction to water-soluble iron(III) sulfate (Fe2(SO4)3).

[0193] The iron sulfate is then allowed to diffuse into the bulk electrolyte solution, optionally passing through a permeable membrane (e.g., a dialysis bag). + is attracted to the negative electrode (anode, e.g., a graphite rod) to produce ammonium hydroxide (NHOH) in the electrolyte solution. Hydrogen ions in the solution are attracted to the cathode, where they produce hydrogen gas. Water-soluble iron(III) sulfate can then undergo a salt metathesis reaction with ammonium hydroxide in solution to produce insoluble iron(III) hydroxide (Fe(OH)) in the form of a reddish-brown precipitate. The reaction in this embodiment can be summarized as follows: (NH4)2SO4 → 2NH4 + +SO4 2- HO → H + +OH - 2H + +2e - → H2 (cathode) NH4 + +OH - → NH4OH Fe → Fe 3+ +3e -( anode) 2Fe III +3SO4 2- → Fe2(SO4)3(water soluble)(anode) NH4OH+Fe2(SO4)3→ 3(NH4)2SO4+2Fe(OH)3(water-insoluble)

[0194] In other embodiments, the iron is precipitated as an iron complex such as jarosite, for example, NH4[Fe(OH)2]3(SO4)2.

[0195] In some embodiments, the salt formed by the redox reaction further comprises a salt metathesis reaction, e.g., in the above formula. In certain embodiments, the salt metathesis reaction forms an insoluble salt. In some embodiments, the insoluble salt formed by the salt metathesis reaction is iron hydroxide. Advantageously, insoluble salts such as iron hydroxide can be a valuable by-product formed during the purification process of the present invention. As previously mentioned, iron hydroxide can be used, for example, as a catalyst for decomposing methane to form graphite and hydrogen gas (e.g., by the Hazer® process).

[0196] In some embodiments, the electrochemical treatment does not affect the morphology of the graphite or damage it at all. Other graphite purification techniques, such as the use of hydrofluoric acid and microwave purification, can damage or change the morphology of the purified graphite. In some embodiments, at least about 70 wt.%, at least about 80 wt.%, at least about 90 wt.%, at least about 95 wt.%, at least about 98 wt.%, or at least about 99 wt.% of the purified graphite, relative to the total graphite including impurities, retains its original morphology and / or is intact prior to the purification process.

[0197] In some embodiments, the process includes the use of a permeable membrane between the cathode and anode during the electrochemical treatment. In certain embodiments, the anode is surrounded by a permeable membrane. In preferred embodiments, the cathode is surrounded by a permeable membrane. In certain embodiments, both the cathode and the anode are surrounded by permeable membranes.

[0198] Alternatively, impurities can be removed from the graphite using electrochemical processes in undivided cells (i.e., without the use of a permeable membrane). The greatest drawback to using undivided cells may be their susceptibility to short circuits, given the conductivity of the graphite and / or electrolyte.

[0199] As will be appreciated by those skilled in the art, any suitable type of permeable membrane can be used in the processes of the present invention. In some embodiments, the permeable membrane is a neutrally charged permeable membrane. In some embodiments, the permeable membrane is an anion exchange membrane. In some embodiments, the permeable membrane is a cation exchange membrane.

[0200] In some embodiments, the permeable membrane (e.g., dialysis tubing) has a molecular weight of less than about 1 million Da, less than about 900,000 Da, less than about 800,000 Da, less than about 700,000 Da, less than about 600,000 Da, less than about 500,000 Da, less than about 400,000 Da, less than about 300,000 Da, less than about 200,000 Da, less than about 100,000 Da, less than about 900 kDa, less than about 800 kDa, less than about 700 kDa, less than about 600 kDa, less than about 500 kDa, less than about 400 kDa, less than about 300 kDa, less than about 200 kDa In one embodiment, the permeable membrane has a molecular weight cut-off (MWCO) of less than about 100 kDa, less than about 90 kDa, less than about 80 kDa, less than about 70 kDa, less than about 60 kDa, less than about 50 kDa, less than about 40 kDa, less than about 35 kDa, less than about 30 kDa, less than about 25 kDa, less than about 20 kDa, less than about 15 kDa, less than about 10 kDa, less than about 7.5 kDa, less than about 5 kDa, less than about 4.5 kDa, less than about 4 kDa, less than about 3.5 kDa, less than about 3 kDa, less than about 2.5 kDa, less than about 2 kDa, less than about 1.5 kDa, or less than about 0.5 kDa. In one embodiment, the permeable membrane has a flow rate of 0.1 to 100 L / min / dm@2 at 200 Pa. 2 Preferably, the permeable membrane has an air permeability of between 1 and 50 L / min / dm at 200 Pa. 2 More preferably, the permeable membrane has an air permeability of between 2 and 30 L / min / dm at 200 Pa. 2 It has an air permeability of .

[0201] In some embodiments, the anion exchange membrane is a phosphonium cation (i.e., PR3 + ), sulfonium cations (i.e., SR2 + ), ammonium cation (NH3 +), where R is independently H, alkyl, aryl, or halide according to the respective definitions provided above.

[0202] In some embodiments, the cation exchange membrane is a membrane that exchanges phosphate anions (i.e., PO - ), sulfonate anion (i.e., SO3 - ), carboxylate anion (i.e., COO - ), C6H4O - ) containing negative charges.

[0203] In certain embodiments, the permeable membrane is selected from the group consisting of asbestos cloth, cellulose, glass cloth, filter cloth, glass cloth impregnated with silica gel, porous sintered stainless steel, vinyl chloride acrylonitrile, polyethylene terephthalate (PET), and combinations thereof. In embodiments, the membrane can be any sintered medium that does not react with the electrolyte, such as sintered PTFE.

[0204] As will be appreciated by those skilled in the art, any suitable electrolyte can be used in the present invention. In some embodiments, the electrolyte is a sulfate salt, a nitrate salt, a chloride salt, and combinations thereof.

[0205] In some embodiments, the electrolyte is selected from the group consisting of ammonium sulfate, sodium sulfate, magnesium sulfate, iron sulfate, copper sulfate, zinc sulfate (ZnSO), zinc chloride (ZnCl), zinc trifluoromethylsulfonate (Zn(CFSO)), cadmium nitrate, cobalt nitrate, sodium nitrate, sodium chloride, nickel chloride, potassium chloride, ammonium chloride (NHCl), calcium chloride, sulfuric acid, and combinations thereof. In other embodiments, the electrolyte can be nitric acid or sulfuric acid.

[0206] In a preferred embodiment, the electrolyte is selected from the group consisting of ammonium sulfate, iron sulfate, and combinations thereof, e.g., ammonium sulfate and sulfuric acid. Advantageously, when iron sulfate is used as the electrolyte in the process of the present invention, elemental iron is formed on the cathode during the electrochemical treatment of graphite. The elemental iron is in the form of dendrites and forms in place of insoluble iron hydroxide. Similarly, elemental iron can be a valuable by-product formed during the refining process of the present invention. For example, iron can also be used as a catalyst for, for example, decomposing methane to form graphite and hydrogen gas (e.g., by the Hazer® process described above).

[0207] Based on preliminary data, the use of iron sulfate as the electrolyte may provide graphite of higher purity compared to the use of ammonium sulfate.

[0208] In certain embodiments, the electrolyte is an ionic liquid. In certain embodiments, the ionic liquid comprises a cation selected from 1-alkyl-3-methyl-imidazolium, N-alkyl-pyridinium, tetraalkyl-ammonium, tetraalkyl-phosphonium, and combinations thereof. In some embodiments, the alkyl group is a C2-C 12 In some embodiments, the ionic liquid comprises a cation selected from the group consisting of 1-ethyl-3-methyl-1H-imidazolium, 1-butyl-3-methyl-1H-imidazolium, 1-butylpyridinium, and combinations thereof.

[0209] In certain embodiments, the process of the present invention involves replacing some or all of the spent electrolyte with fresh electrolyte (i.e., new electrolyte that has not been used in the process). In certain embodiments, the partial or complete replacement of the electrolyte can be done by a batch process or a continuous process.

[0210] In certain embodiments, the electrolyte solution has any suitable pH. In some embodiments, the pH of the electrolyte solution is between about 1 and 10, between about 6 and 8, between about 8 and 10, preferably between about 1 and 6, between about 1 and 5, and more preferably between about 1 and 3. In preferred embodiments, the pH of the electrolyte solution is less than about 6, less than about 5, and preferably less than about 3.

[0211] In certain embodiments, the electrolyte solution has a concentration between about 0.01 and 10 M. For example, the electrolyte solution has a concentration of about 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.95, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, or about 10 M.

[0212] In some embodiments, the electrolyte solution preferably has a concentration of between about 0.01 and 5 M, between about 0.01 and 3 M, between about 0.01 and 2 M, between about 0.01 and 1 M, between about 0.01 and 0.5 M, between about 0.05 and 1 M, between about 0.05 and 0.5 M, between about 0.05 and 0.3 M, preferably between about 0.05 and 0.15 M. Most preferably, the electrolyte solution has a concentration of about 0.1 M.

[0213] Any suitable solvent for dissolving the electrolyte can be used in the process of the present invention. Typically, the electrolyte is an aqueous solution.

[0214] In certain embodiments, the solvent is water, an organic solvent, an inorganic non-aqueous solvent, and combinations thereof. In other embodiments, the solvent may be polar. In preferred embodiments, the dispersion medium is selected from the group consisting of water, glycerin, glycerol, cellulose ethers, and combinations thereof.

[0215] Suitable organic solvents may be selected from the group consisting of pentane, cyclopentane, hexane, cyclohexane, benzene, toluene, 1,4-dioxane, chloroform, diethyl ether, dichloromethane, tetrahydrofuran, ethyl acetate, acetone, dimethylformamide, acetonitrile, dimethyl sulfoxide, nitromethane, propylene carbonate, n-butanol, isopropanol, n-propanol, ethanol, methanol, formic acid, acetic acid, hexafluoroisopropanol, trifluoroacetic acid, and combinations thereof.

[0216] Suitable inorganic solvents may be selected from the group consisting of liquid ammonia, liquid sulfur dioxide, sulfuryl chloride, sulfuryl chloride fluoride, phosphoryl chloride, dinitrogen tetroxide, antimony trichloride, bromine pentafluoride, hydrogen fluoride, pure sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, boric acid, hydrofluoric acid, hydrobromic acid, perchloric acid, hydroiodic acid, and combinations thereof.

[0217] In certain embodiments, the electrolyte can be dissolved in a mixture of two or more miscible solvents, for example, a mixture of water and an aqueous solvent, or a mixture of an organic and an aqueous solvent.

[0218] The process of the present invention can be carried out at any suitable temperature. In some embodiments, the process is carried out at a temperature between about 5°C and about 200°C, between about 5°C and about 100°C, between about 5°C and about 80°C, between about 5°C and about 50°C, between about 50°C and about 100°C, between about 60°C and about 90°C, between about 70°C and about 80°C, or between about 5°C and about 30°C. In some embodiments, the process is carried out at a temperature less than about 100°C, less than about 80°C, less than about 50°C, and preferably less than about 30°C. In preferred embodiments, the process is carried out at about 25°C, or between 70°C and 80°C. In some embodiments, the process is carried out at a temperature less than about 100, 90, 80, 70, 60, 50, 40, 30, 20, or 10°C.

[0219] In some embodiments, the predetermined temperature is between about 5°C and about 200°C, between about 5°C and about 100°C, between about 5°C and about 80°C, between about 5°C and about 50°C, between about 50°C and about 100°C, between about 60°C and about 90°C, between about 70°C and about 80°C, or between about 5°C and about 30°C. In some embodiments, the predetermined temperature is less than about 100°C, less than about 80°C, less than about 50°C, and preferably less than about 30°C. In preferred embodiments, the predetermined temperature is about 25°C or between 70°C and 80°C. In some embodiments, the predetermined temperature is less than about 100, 90, 80, 70, 60, 50, 40, 30, 20, or 10°C.

[0220] In embodiments, the cell may be pressurized at between about 1 and about 100 bar(g), between about 5 and 90 bar(g), between about 10 and 80 bar(g), between about 15 and 70 bar(g), between about 20 and 60 bar(g), between about 25 and 50 bar(g), between about 30 and 40 bar(g), or about 35 bar(g).

[0221] In some embodiments, the impurities are naturally occurring, e.g., natural impurities from geological formations such as mined graphite, hi some embodiments, the impurities are synthetically occurring, e.g., the impurities are introduced as a result of synthetically producing graphite.

[0222] As can be appreciated by those skilled in the art, any suitable graphite containing impurities selected from metals, metal oxides, and combinations thereof can be used in the purification process of the present invention. In certain embodiments, the graphite is naturally occurring. In preferred embodiments, the graphite is synthetically occurring, such as produced by the Hazer® process described above.

[0223] As will be appreciated by those skilled in the art, graphite can exist in many forms, including graphite fibers, e.g., anisotropic nanofibers (ANFs), which are fibrous carbon structures typically ranging in length from 100 nm to 100 microns (also encompassing carbon nanotubes (CNTs), which are cylindrical nanostructures containing single or multiple graphite sheets aligned concentrically or perpendicularly to a central axis); carbon nano-onions (CNOs), which are structures consisting of multiple spherical graphite sheets concentrically layered around a central core, typically a catalyst particle or void; and carbon microspheres (CMS), which can be hollow spherical graphite structures or graphite concentrically layered around a central core, typically larger than 500 nm in size, and which are spherical in shape, but can also be chain-like. As noted above, the morphology of synthetic graphite can be controlled as described in the process of WO 2017 / 031529.

[0224] In certain embodiments, the graphite can have shapes such as flake-like, sphere-like, needle-like, plate-like, wire-like, tube-like, whisker-like, ball-like, nanographite, tubes, wires, and combinations thereof.

[0225] The graphite used in the process of the present invention has an average size (d) ranging between about 10 nm and 350 μm, for example, 10 nm to 1 μm, or 1 μm to 65 μm, or 100 nm to 10 μm. 50) can be used. For example, graphite having an average size of about 10 nm to 1000 nm can be used. For example, graphite having an average size of 10 nm to 100 nm, or 50 nm to 250 nm, or 200 to 500 nm, or 500 to 1000 nm, or 400 to 750 nm, e.g., 10 nm, 50 nm, 100 nm, 500 nm, or 1000 nm can be used. Graphite having an average size in the range of about 1 μm to 350 μm can also be used. For example, 1 μm to 45 μm, or 40 μm to 60 μm, or 20 μm to 40 μm, or 30 μm to 50 μm, or 40 μm to 50 μm, or 40 μm to 60 μm, or 50 μm to 100 μm, or 100 μm to 250 μm, or 200 μm to 350 μm, or less than 300, less than 200, less than 100, less than 65, less than 60, less than 55, less than 50 Graphite having an average size of less than, less than 45, less than 40, less than 35, less than 30, less than 25, less than 20, less than 15, less than 10, or less than 5 μm, or 350, 300, 250, 200, 150, 100, 85, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 4, 3, 2 or 1 μm may be used.

[0226] The graphite used in the process of the present invention has a particle size of about 1 to about 1000 m 2 / g, approximately 1 to 700 m 2 / g, approximately 1 to approximately 400 m 2 / g. For example, graphite can have a surface area between 1 and 5 m 2 / g or 1 to 10 m 2 / g or 5 to 20 m 2 / g or 20-30m 2 / g or 15-25m 2 / g or 1 to 30m 2 / g, for example, 1, 2, 3, 4, 5, 10, 12.5, 15, 17.5, 20, 22.5, 25, 27.5 or 30 m 2 The graphite may be a low surface area graphite having a surface area of ​​50 to 400 m / g. 2 / g, for example, 100-150m 2 / g or 100-200m2 / g or 50-200m 2 / g or 150-250m 2 / g or 200-375m 2 / g or 250-350m 2 / g or 300-400m 2 / g or 100-400m 2 / g, for example, 50, 100, 120, 140, 160, 180, 200, 220, 240, 260, 280, 300, 320, 340, 360, 380, or 400 m 2 In some embodiments, the graphite may be a high surface area graphite having a surface area of ​​300 m / g. 2 / g or less than 200m 2 / g or less than 100m 2 / g。 The surface area may be N2 (NSA) BET surface area. Nitrogen adsorption measurements at liquid nitrogen temperatures can be used to characterize the total surface area of ​​the graphite herein based on the Brunauer, Emmett, and Teller (BET) theory of multilayer gas adsorption (see also ASTM method D6556-04).

[0227] The graphite used herein preferably has a crystallinity of between about 60% and 99.9%, for example, between 60 and 80%, or between 75 and 90%, or between 85 and 99%, or between 90 and 99%, or between 95 and 99%, and for example, graphite having a crystallinity of at least 60%, at least 70%, at least 80%, at least 85%, at least 90%, at least 95%, at least 99%, or at least 99.9%, for example, 60%, 70%, 80%, 85%, 90%, 95%, 99%, or 99.9%.

[0228] The graphite used in the process of the present invention preferably has a resistivity of less than about 1.0 Ω.cm, less than about 0.8 Ω.cm, less than about 0.5 Ω.cm, less than about 0.1 Ω.cm, or less than about 0.05 Ω.cm, for example, between 0.01 and 0.05, or between 0.05 and 0.10, or between 0.05 and 0.15, or between 0.10 and 0.20, or between 0.15 and 0.25, or between 0.25 and 0.4, or between 0.20 and 0.50, or between about 0.4 and 0.65, or between 0.50 and 0.75, or between 0.75 and 1.0, or between 0.01 and 1 Ω.cm. For example, the graphite may have a resistivity of 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1.0 ohm-cm.

[0229] In some embodiments, the graphite can be natural graphite, synthetic graphite, amorphous graphite, calcined petroleum coke, crystalline flake graphite, natural flake graphite, surface-enhanced flake graphite, expandable graphite, refined flake graphite, refined crystalline flake graphite, refined petroleum coke, refined synthetic graphite, refined vein graphite, synthetic graphite, primary artificial graphite, secondary artificial graphite, spherical natural graphite, vein graphite, and combinations thereof.

[0230] The graphite used herein preferably has a carbon content of between about 5% and 99.9%, for example, between 60 and 80%, or between 75 and 90%, or between 85 and 99%, or between 90 and 99%, or between 95 and 99%, e.g., a carbon content of at least 60%, at least 70%, at least 80%, at least 85%, at least 90%, at least 95%, at least 99%, or at least 99.9%, e.g., graphite having a carbon content of 60%, 70%, 80%, 85%, 90%, 95%, 99%, or 99.9% is preferred.

[0231] In some embodiments, the purified graphite has a purity of greater than about 90%, preferably greater than 95%, more preferably greater than 98%, and even more preferably greater than 99%.

[0232] In some embodiments, the purified graphite has an impurity concentration of less than 15% w / w, preferably less than 10%, preferably less than 5%, more preferably less than 3%, more preferably less than 2%, and even more preferably less than 1%.

[0233] It should be appreciated that electrodes used as anodes or cathodes can be made from any suitable conductive material. In some embodiments, the electrodes are made from a metal or metal alloy. In some embodiments, the electrodes are made from a material selected from the group consisting of electroceramics, copper, aluminum, platinum, titanium, gold, silver, iron, steel, stainless steel, brass, bronze, nickel, lead, lead alloys, conductive rubber, conductive carbon, such as graphite, graphene, and reduced graphene oxide, and combinations thereof. In some embodiments, the electrodes can include a coating of another conductive material. In other embodiments, the electrodes can be non-metallic electrodes, such as graphite, conductive polymers, conductive ceramics, and other conductive materials suitable for constructing or coating electrodes (or the like).

[0234] It should also be appreciated that the electrodes used as anodes or cathodes can have any suitable thickness. In certain embodiments, the electrodes have a thickness of about 1 mm to about 30 mm, about 1 mm to about 20 mm, or about 5 mm to about 15 mm.

[0235] In some embodiments, the process of the present invention uses multiple cathodes. In some embodiments, the process includes the use of 2, 3, 4, 5, 6, 7, 8, 9, 10 (or more) cathodes. In some embodiments, the process includes the use of between 2 and 50 cathodes, between 2 and 40 cathodes, between 2 and 30 cathodes, between 2 and 20 cathodes, and between 2 and 10 cathodes.

[0236] In some embodiments, the process of the present invention uses multiple anodes. In some embodiments, the process includes the use of 2, 3, 4, 5, 6, 7, 8, 9, 10 (or more) anodes. In some embodiments, the process includes the use of between 2 and 50 anodes, between 2 and 40 anodes, between 2 and 30 anodes, between 2 and 20 anodes, and between 2 and 10 anodes.

[0237] As will be appreciated by those skilled in the art, the process of the present invention can be carried out using any suitable voltage. In certain embodiments, the process is carried out at a voltage between about 5 and 300 V, between about 5 and 240 V, between about 5 and 220 V, between about 5 and 200 V, between about 5 and 150 V, between about 5 and 100 V, between about 5 and 50 V, between about 5 and 30 V, between about 5 and 24 V, or between about 5 and 12 V.

[0238] In a preferred embodiment, the process of the present invention is carried out using direct current. In a preferred embodiment, the process of the present invention is carried out using alternating current.

[0239] In certain embodiments, the process of the present invention can be carried out for between about 1 hour and 2 weeks, between about 1 hour and 1 week, between about 1 hour and 5 days, between about 1 hour and 4 days, between about 1 hour and 3 days, between about 1 hour and 96 hours, between about 1 hour and 48 hours, between about 6 hours and 48 hours, between about 12 hours and 48 hours, or between about 24 hours and 48 hours.

[0240] In some embodiments, the process of the present invention is a batch process. In some embodiments, the process of the present invention is a continuous process. In other preferred embodiments, the process of the present invention can be carried out on a continuous basis by periodic or constant circulation of the electrolyte, addition of crude graphite, and extraction of purified graphite. In some embodiments, the crude graphite can be recycled back into the electrochemical cell for further purification.

[0241] In certain embodiments, the process of the present invention further comprises a washing and / or sonication step to remove further impurities, hi certain embodiments, the process of the present invention further comprises a filtration step to remove impurities, such as using a 0.45 μm filter or centrifugation.

[0242] As will be appreciated by those skilled in the art, the process of the present invention can further include one or more additional purification steps. For example, the purified graphite may be further subjected to acid washing, base washing, heat treatment, or a combination thereof to increase the carbon purity beyond that obtained by the process of the present invention. In some embodiments, graphite material pretreated by acid washing and ultrasonic treatment steps has a purity of about 96.3%. In certain embodiments, the purity is further increased by another ECP process.

[0243] In certain embodiments, the process of the present invention comprises a plurality of electrochemical cells. In some embodiments, the process comprises the use of 2, 3, 4, 5, 6, 7, 8, 9, 10 (or more) electrochemical cells. In these embodiments, the electrochemical cells can be connected in series or in parallel. Each electrochemical cell comprises at least one cathode and at least one anode.

[0244] Graphite Slurry Solution Prior to the present improvements, the inventors conducted experiments by packing graphite into dialysis bags. However, significant difficulties existed in bulk handling of packed graphite, which could be alleviated by using graphite slurries. Therefore, the feasibility of using graphite slurries in an ECP process was investigated. The experimental setup was designed similarly to the above experiment, but the contents were reversed: 1.0 M (NH4)2SO4 electrolyte and a graphite rod (cathode) were placed in the dialysis bag. Hazer graphite was made into a 16% volume slurry solution with 1.0 M (NH4)2SO4 electrolyte. A platinum wire was inserted directly into the graphite solution, and the ECP process was operated for 24 hours. The setup is shown in Figure 12. The slurry experiments revealed several interesting findings, discussed below, and thus provided Hazer with several parameters to consider when designing an upscale purification system.

[0245] Figure 12b shows the setup for the slurry experiment after 1 hour and 24 hours. During this process, the formation of a red sludge could be seen in the graphite solution and in the dialysis bag. A significant decrease in current was also observed when performing ECP of the graphite slurry. Because there is an inverse relationship between resistivity and current at a constant voltage, this suggests that the resistivity of the graphite slurry was higher than that of the packed graphite. This may have slowed the reaction rate and required a longer reaction time to reach a comparable level of purity.

[0246] During the ECP process, Fe to Fe 3+ +3e - The ionization of iron to HCl is essential for purification. The power required for this reaction can be modeled using the conversion of 1 kg of iron. 1 kg of iron corresponds to 17.86 moles of Fe, and 3 e per mole of Fe. - is required, 53.57 moles e - Therefore, the power required is:

number

[0247] Based on these results, tests were conducted to determine other necessary parameters. Resistivity tests showed that adding electrolyte to the packed graphite significantly reduced its conductivity. Tests were conducted in a three-cell system, with a glass frit separating the two other chambers.

[0248] Using a three-cell system, current tests were performed with a multimeter to examine the effect of electrode distance. As the electrodes were moved farther apart, the current clearly decreased from 0.3 mA to 0.03 mA.

[0249] The effect of increasing voltage was investigated in a three-cell system. By increasing the voltage while maintaining the set electrode distance, a gradual increase in current could be observed. Increasing the voltage from 10 V to 20 V increased the current from 0.064 A to 0.145 A. Importantly, this represents a 27% improvement over the current increase expected from increasing voltage, implying a decrease in the resistance of the system. The overall increase in current provides more power to the cells, thus enhancing the reaction rate.

[0250] Iron by-products (red sludge) Understanding the state of iron is necessary to remove the iron by-product (red sludge) as part of the development and scaling of ECP. To this end, two different analytical techniques were used to examine the iron by-product generated during the ECP process: TGA and Raman spectroscopy. Both techniques indicated that the iron by-product is more complex than Fe(OH)3.

[0251] The TGA spectrum in Figure 13 shows that there are multiple stages in the weight loss of the iron sludge, similar to what has been seen in other research papers investigating ammonium jarosite ((NH4)Fe3(SO4)2(OH)6). The stages of thermal decomposition observed in ammonium jarosite, as described by Frost et al. [Thermal decomposition of ammonium jarosite (NH4Fe3(SO4)2(OH)6); J Therm Anal Calorim 84, 489-496 (2006). DOI: 10.1007 / s10973-005-6953-8], can also be observed in the TGA spectrum of Hazer® graphite.

[0252] Furthermore, Raman spectroscopy of dried iron sludge (oven dried at 50 °C; not shown) showed that the sample consisted of various iron oxide species. The observed peaks suggest the presence of Fe2O3, Fe3O4, and graphite. The presence of Fe3O4 has not previously been observed in Hazer® graphite. SO4 2- Peaks (approximately 1005 and 1094 cm -1 ) was not observed, this may be an unexpected hydrothermal phase transformation at low temperatures due to the presence of iron sulfate.

[0253] The results of these tests suggest that the red sludge is an iron complex, possibly ammonium jarosite. Iron oxide can be recovered from jarosite by thermal treatment at temperatures above 550 °C, according to TGA. Therefore, iron species recovered from graphite can be used as a high-purity catalyst.

[0254] It was observed that most of the red sludge or jarosite aggregated on the outside of the dialysis bag and then settled as sediment. However, such aggregation is expected to occur within the dialysis bag as well. Therefore, to obtain high-purity graphite, it may be necessary to separate and remove the jarosite from the carbon. While physical separation by centrifugation was unsuccessful, particles loosely attached to the graphite surface were removed by vacuum filtration and washing, resulting in a purity of 99.5%. A method for removing jarosite, a basic hydrous sulfate material, from graphite can be to solubilize the material in an acid such as H2SO4.

[0255] To determine whether H2SO4 washing could be an alternative to time-consuming vacuum filtration washing, 0.1 M H2SO4 was added to iron sludge collected from the electrolyte at a 1:4 ratio. The mixture of H2SO4 and Fe sludge was clearer compared to the control where DI water was added. After 15 hours (overnight), the Fe sludge mixed with H2SO4 was clear, unlike the control where the Fe sludge settled.

[0256] This experiment demonstrated that H2SO4 digests iron-based sludge, resulting in a less aggressive and time-consuming cleaning procedure. Depending on the preferred design for upscaling this technology, the results provide directional information for downstream cleaning processes in the upscale design. Optimizing the addition of H2SO4 to remove excess jarosite and determining the removal rate and concentration required for its removal may further elucidate the findings of this invention.

[0257] The iron by-product (red sludge) collected from the above experiment was tested as a potential catalyst for the Hazer® pyrolysis process. This test was performed using a TGA-EG with 100% methane flow at 900°C, 1 atmosphere, and 8 hours of reaction time (Figure 14). Performance was then compared to the top two catalysts found in Table 2 below: Sample XG (synthetic iron oxide) and Sample E (iron ore).

[0258] [Table 2]

[0259] As shown in Table 2, the complete reduction of the iron by-product (red sludge) in the Hazer® process was significantly longer than that of the other catalysts. This may be due to the complex structure of the iron by-product, as detailed above. Interestingly, the average reaction rate of the iron by-product was the same as that of Sample E. It is noteworthy that the tested iron by-product was collected during the purification of a sample originally synthesized from Sample E. This catalyst exhibited superior catalytic activity in the high-rate region compared to the other two catalysts. It is theorized that this may be related to the significantly altered catalyst / crystal size, surface area, and significantly higher iron purity at the fully reduced state of the red sludge, as the purification process significantly altered Sample E.

[0260] Utilizing different electrolytes in the described ECP process may improve the efficiency of the reaction kinetics. The choice of electrolyte depends on the electrolyte's ability to react with iron during the ECP process to form iron sulfate or other iron-soluble structures and the ease of removal from the purified graphite. Sulfuric acid is commonly used as an electrolyte due to its high conductivity and ability to provide a large proton density during the electrochemical reaction, enhancing the reaction rate. To determine the efficiency of H2SO4 as an electrolyte for the ECP process, experiments were performed as described above. However, the electrolyte was replaced with 0.1 M H2SO4.

[0261] Initial observations included the generation of large amounts of gas bubbles, likely due to the production of H2 and O2 from the electrochemical reaction.

[0262] Iron(II) sulfate was the second candidate tested. FeSO4 has a number of advantages, including the production of elemental iron (Fe) by-product, which can be reused as a catalyst, and a relatively simple side reaction; the electrolyte used was 0.1 M FeSO4. The experiment was run for 24 hours. [ka]

[0263] The FeSO4 electrolyte was initially cloudy yellow, but after 1 hour of ECP, the solution turned clear yellow. Small gray particles were observed at the bottom of the beaker, and dendrite growth was observed on the carbon rod. After 3 hours, the electrolyte became clear, and more dendrite growth could be observed on the surface of the carbon rod cathode. These dendrites were likely Fe, which could be collected and optionally reused as a catalyst in the Hazer® process.

[0264] Comparing the TGA results of the various electrolytes, their efficiency was very similar. All electrolytes were able to purify graphite from 80% to over 93% in 24 hours. The differences in the final purity of the graphite were small enough to be considered within the experimental error range. Therefore, the effectiveness of the purification was not affected by the choice of electrolyte. Instead, when considering electrolytes, commercial viability, including catalyst recovery ability, reaction rate enhancement, and / or electrolyte cost, appears to be of paramount importance. This would require a proper techno-economic analysis to determine the preferred electrolyte.

[0265] Refined graphite In another aspect, the present invention provides purified graphite comprising impurities selected from metals, metal oxides, and combinations thereof, wherein the purified graphite has an impurity concentration of less than 20% w / w.

[0266] In some embodiments, the purified graphite has an impurity concentration of less than 15% w / w, preferably less than 10%, preferably less than 5%, more preferably less than 3%, more preferably less than 2%, more preferably less than 1%, more preferably less than 0.1%, and most preferably less than 0.05% w / w.

[0267] In some embodiments, the purified graphite has a purity of greater than about 90%, preferably greater than 95%, more preferably greater than 98%, and even more preferably greater than 99%.

[0268] In some embodiments, the purified graphite has a carbon purity of greater than about 90%, preferably greater than 95%, more preferably greater than 98%, and even more preferably greater than 99%.

[0269] In certain embodiments, the purified graphite can have shapes such as flake-like, sphere-like, needle-like, plate-like, wire-like, tube-like, whisker-like, ball-like, nanographite, tubes, wires, and combinations thereof.

[0270] In some embodiments, the purified graphite of the present invention has an average size (d) ranging between about 10 nm and 350 μm, e.g., 10 nm to 1 μm, or 1 μm to 65 μm, or 100 nm to 10 μm. 50 For example, the purified graphite of the present invention may have an average size of between about 10 nm and 1000 nm, for example, the purified graphite may have an average size of between 10 nm and 100 nm, or between 50 nm and 250 nm, or between 200 and 500 nm, or between 500 and 1000 nm, or between 400 and 750 nm, e.g., 10 nm, 50 nm, 100 nm, 500 nm, or 1000 nm. The purified graphite of the present invention has an average size ranging between about 1 μm and 350 μm, for example, the purified graphite may be 1 μm to 45 μm, or 40 μm to 60 μm, or 20 μm to 40 μm, or 30 μm to 50 μm, or 40 μm to 50 μm, or 40 μm to 60 μm, or 50 μm to 100 μm, or 100 μm to 250 μm, or 200 μm to 350 μm, or less than 300 μm. less than 200, less than 100, less than 65, less than 60, less than 55, less than 50, less than 45, less than 40, less than 35, less than 30, less than 25, less than 20, less than 15, less than 10 or less than 5 μm, or 350, 300, 250, 200, 150, 100, 85, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 4, 3, 2 or 1 μm.

[0271] The purified graphite of the present invention has a viscosity of about 1 to about 1000 m 2 / g, approximately 1 to 700 m 2 / g, approximately 1 to 400 m 2 For example, the purified graphite may have a surface area between 1 and 5, or between 1 and 10, or between 5 and 20, or between 20 and 30, or between 15 and 25, or between 1 and 30 m 2 / g, for example, 1, 2, 3, 4, 5, 10, 12.5, 15, 17.5, 20, 22.5, 25, 27.5 or 30 m 2 The graphite may be a low surface area graphite having a surface area of ​​50 to 400 m / g. 2 / g, for example, between 100 and 150, or between 100 and 200, or between 50 and 200, or between 150 and 250, or between 200 and 375, or between 250 and 350, or between 300 and 400, or between 100 and 400m 2 / g, for example, 50, 100, 120, 140, 160, 180, 200, 220, 240, 260, 280, 300, 320, 340, 360, 380, or 400 m 2 In some embodiments, the purified graphite may be a high surface area graphite having a surface area of ​​300 m / g. 2 / g or less than 200m 2 / g or less than 100m 2 / g。 The surface area may be N2 (NSA) BET surface area.

[0272] The purified graphite of the present invention preferably has a crystallinity of about 60% to 99.9%, for example, 60 to 80%, or 75 to 90%, or 85 to 99%, or 90 to 99%, or 95 to 99%, and for example, at least 60%, at least 70%, at least 80%, at least 85%, at least 90%, at least 95%, at least 99%, or at least 99.9%, for example, 60%, 70%, 80%, 85%, 90%, 95%, 99%, or 99.9% crystallinity is preferred.

[0273] The purified graphite of the present invention preferably has a resistivity of less than about 1.0 Ω.cm, less than about 0.8 Ω.cm, less than about 0.5 Ω.cm, less than about 0.1 Ω.cm, or less than about 0.05 Ω.cm, for example, between 0.01 and 0.05, or between 0.05 and 0.10, or between 0.05 and 0.15, or between 0.10 and 0.20, or between 0.15 and 0.25, or between 0.25 and 0.4, or between 0.20 and 0.50, or between about 0.4 and 0.65, or between 0.50 and 0.75, or between 0.75 and 1.0, or between 0.01 and 1 Ω.cm. For example, the purified graphite can have a resistivity of 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1.0 Ω.cm.

[0274] The purified graphite of the present invention preferably has a carbon content of about 60% to 99.9%, for example, between 60% and 80%, or between 75% and 90%, or between 85% and 99%, or between 90% and 99%, or between 95% and 99%, e.g., at least 60%, at least 70%, at least 80%, at least 85%, at least 90%, at least 95%, at least 99%, or at least 99.9%, e.g., 60%, 70%, 80%, 85%, 90%, 95%, 99%, 99.9%, or 99.95% carbon content is preferred.

[0275] As can be appreciated by those skilled in the art, the purity of graphite that has undergone the process of the present invention can be determined both before and after treatment using any suitable technique known in the art. For example, suitable techniques for measuring carbon purity are thermogravimetric analysis (TGA) or atomic emission spectroscopy (e.g., inductively coupled plasma atomic emission spectroscopy, which can also determine the amount of impurities). [Example]

[0276] Example 1: Production of impure synthetic graphite Iron oxide is used as a catalyst for the decomposition of methane to produce graphite. Two types of high-grade iron oxides were used: hematite (99%, <5 μm, Sigma-Aldrich) and magnetite (95%, <5 μm, Sigma-Aldrich), along with two iron ore samples: hematite ore (Pilbara mine) and goethite ore (Yandi mine). The ore samples were crushed to less than 150 μm but were otherwise unprocessed. The "as received" compositional data, particle size distribution, and surface area of ​​all samples are detailed in Table 3.

[0277] [Table 3]

[0278] Each sample was placed in a separate single-stage reactor. The reactor was a 1 / 2 inch (1.27 cm) diameter vertical stainless steel (SS316 Swagelok) tube with an internal liner of 3 / 8 inch (0.95 cm) quartz tubing. The internal liner of the quartz tube reduces the catalytic effect of the stainless steel reactor wall by limiting contact with the reactive methane gas. Catalyst samples (20 g) were placed inside the 3 / 8 inch "test tube-like" quartz tube.

[0279] Each sample is 10 cm 3 The reaction was carried out at temperatures ranging from 750 to 950 °C using pure methane (UHP) / min and a reaction pressure between 1 and 9 bar (absolute). After complete deactivation (approximately 19 hours), the reaction was terminated and 20 cm 3 The sample was cooled by pure nitrogen (UHP) at 1000 W / min. The resulting graphitic carbon (and the catalyst particles embedded as impurities) was weighed to determine the total carbon yield per gram of iron catalyst used.

[0280] Low-grade iron ore samples performed nearly as well as high-grade oxides to produce graphite, with carbon yields ranging from 9.2 to 8.9 grams of carbon per gram of iron, corresponding to carbon purities of 90 wt% to 89 wt%, respectively.

[0281] Example 2: Plant for the purification of graphite An electrochemical cell such as that shown in FIG. 1 was used. The cell included a permeable membrane (e.g., a belt filter cloth) to separate the anode and cathode. A constant supply of fresh catholyte (i.e., catholyte not used in the purification process) was pumped through the cathode, which was constructed of stainless steel. A mixture of fresh anolyte and an impure graphite slurry was pumped through the anode, which was constructed of a lead alloy, and the mixture was constantly stirred using a stirrer. The catholyte and anolyte may be the same or different.

[0282] The cathode consisted of three stainless steel plates, and the anode consisted of four lead alloy plates. Impurity-containing graphite slurry was restricted from contacting the cathode via a permeable membrane. The catholyte and anolyte were ferrous sulfate solutions (0.1 M). Iron ions formed as a result of redox reactions during the electrochemical process could permeate the permeable membrane and, together with elemental iron on the cathode, form insoluble iron hydroxide particles. Inlet and outlet flow dividers were installed in the cell to prevent the formation of "dead" zones above the cathode and anode.

[0283] The temperatures of the catholyte and anolyte were maintained at approximately 70-80°C using a water bath. A positive voltage of +10 V was applied to the anode. Then, the purified graphite was collected together with the anolyte, and the iron particles were collected together with the catholyte, as shown in Figure 1.

[0284] Figure 2 shows a block diagram of an electrochemical refining plant capable of accommodating commercial capacities as needed, for example, 1 metric ton, 5 metric ton, 10 metric ton, 15 metric ton, or 20 metric tonnes per day of graphite product with a target purity of greater than 99.5 wt%. As described above, the graphite was delivered and processed as a slurry, and the system alternated between two electrochemical cells in a batch process. In this system, the filtration equipment was common to both cells. The precipitated or removed iron was not left on the graphite.

[0285] An alternative configuration is shown in Figure 3, which is a flowsheet for a commercial-scale graphite refinery plant. The system is designed to accommodate, for example, up to 1 metric ton of graphite product per day.

[0286] Yet another configuration is shown in Figure 4. Below is provided a description of the operation of the major equipment for the ECP process (ECPP).

[0287] Preparation of reagents The ammonium sulphate solid was transferred from a bulker bag to a 10m jar containing fresh Perth Tap Water (PTW). 3 The mixture is discharged into a stirring and mixing tank, where ammonium sulfate is dissolved.

[0288] 15m 3 The ammonium sulphate tank storage tank is refilled from this mixing tank as required, refilling the reagent adjustment tank as required, and then the pre-leach tank 1 with the required ammonium sulphate dosing rate.

[0289] Graphite Feeding and Pre-Leach Unit Operation Graphite is 10m from the Hazer process 3 It is expected to be conveyed into a hopper, which contains an internal 20mm x 20mm safety / debris screen designed to remove any debris that may have been carried over from the Hazer process. 3The hopper is covered to minimize the ingress of moisture and contaminants.

[0290] The graphite is then screw fed into a feed vortex mixer designed to adequately wet the graphite before it is sent to the first pre-leach tank using recycled process water.

[0291] The ammonium sulfate solution is pumped through an in-line solution heater for 15 minutes to raise the temperature to approximately 70°C before being dosed into pre-leach tank 1. 3 It is supplied from an ammonium sulfate tank. During test work on the pre-leach circuit, insufficient heat from the acid addition reaction required adding heat to the circuit to maintain the slurry at the target temperature.

[0292] Nitric acid is also dosed into Pre-Leach Tank 1 at the required flow rate. Nitric acid is necessary to prevent graphite foaming, which caused significant material handling problems and it was concluded that without the addition of nitric acid, the graphite slurry would not flow effectively through the pre-leach tank.

[0293] The slurry flows by gravity through pre-leach tanks 1 to 3 and is then pumped into the ECPP circuit. The temperature of the pre-leach circuits is maintained by immersion heaters (designed from titanium to withstand the acidic environment and set at a set point of 70°C). Each pre-leach tank is agitated using overhead agitators to maintain a uniformly suspended slurry.

[0294] Each tank is capped and vented to the top of the building to remove fumes generated by the process.

[0295] Operation of ECPP cells Each ECPP cell contains a single anode in a central section separated by a filter cloth, which acts as a membrane, allowing only solution and ions to pass between the inner section and two outer sections. Each outer section contains a cathode. The slurry in the central anode section is suspended by two overhead stirrers (one on each side of the anode) to maintain a uniform slurry within this section. A positive charge is applied to the central anode section, and a negative charge is applied to each of the cathodes. Each cell is capped and vented to the top of the building to remove fumes generated by the process.

[0296] Slurry from the pre-leach circuit is discharged into the central anode section of ECPP cell 1, and liquid containing precipitated iron (iron slurry) from ECPP cell 2 is fed into both outer sections of ECPP cell 1. Sulfuric acid is also pumped into the anode section of ECPP cell 1 at a controlled rate.

[0297] The iron slurry from the ECPP cell 1 cathode is pumped to an iron precipitate thickener tank, and the slurry from the inner anode section is pumped to ECPP cell 2 at a controlled rate (same as the pre-leach discharge rate).

[0298] The anode section slurry is pumped to the next ECPP cell, also at a controlled rate, until it is pumped from ECPP cell 4 to a graphite thickener. The purpose of pumping the anode section slurry further down the circuit is to reduce the concentration of iron and the need for subsequent iron washing in downstream graphite filters.

[0299] Ammonium sulfate solution, sulfuric acid, and nitric acid are dosed into the recycle equalization tank along with recycled process water. The recycled process water is pumped into both cathode sections of ECPP cell 4, and most of the dissolved iron in solution is expected to precipitate as ammonium iron sulfate due to the increased pH in the cathode sections. ECPP test runs resulted in an increase in pH in the outer cathode section due to hydrogen generation at the cathode, followed by iron precipitation. The iron slurry from each cathode section is pumped into the preceding ECPP cathode section until it is discharged into the iron precipitate thickener tank as previously described.

[0300] Graphite thickener The anode discharge slurry from ECPP cell 4 is fed to a graphite thickener tank. A predetermined amount of flocculent is dosed into the graphite thickener tank, causing the graphite slurry to settle and produce a slurry with an increased solids content. This slurry is pumped from the bottom of the thickener tank as concentrated slurry (underflow) to a graphite filter. The thickener overflow, containing a liquid with a low concentration of total suspended solids, is discharged to a process liquid collection tank.

[0301] Graphite Filter The underflow from the graphite thickener is pumped to an agitated surge tank and then to a plate and frame vacuum filter where it is filtered into a cake. Once filtered, it is washed with a 5% sulfuric acid solution to remove any dissolved iron contained in the liquid contained within the filter cake. It is then washed with PTW to raise the pH of the liquid within the cake and remove any inherent sulfuric acid. The initial filtrate, along with both wash solutions, is sent to a collection tank for recycle, with the majority being recycled within the Hazer ECPP circuit.

[0302] The washed filter cake is discharged into a hopper and then screw fed into a graphite flash dryer.

[0303] Graphite flash dryer and baghouse The graphite is fed into a graphite flash dryer which produces a dry product that is discharged into a baghouse. The baghouse packages the dried graphite into 1m3 bulker bags which are then transported to the baghouse storage zone.

[0304] Iron sediment thickener The anode discharge iron slurry from ECPP cell 1 is fed to an iron precipitate thickener tank. A predetermined amount of flocculant is dosed to the iron precipitate, causing it to settle and produce a slurry with an increased solids content. This slurry is pumped from the bottom of the thickener tank as concentrated slurry (underflow) to the iron precipitate filter. The thickener overflow, containing a liquid with a low concentration of total suspended solids, is discharged to a process liquor collection tank.

[0305] Iron Sediment Filter The underflow of the iron precipitate thickener is pumped to an agitated surge tank and then to a plate and frame vacuum filter where it is filtered into a cake. The filtrate is sent to a collection tank for recycle, with the majority being recycled within the Hazer ECPP circuit.

[0306] The filter cake is discharged into a hopper and then screw fed into a flash dryer.

[0307] Iron precipitate flash dryer and baghouse The iron precipitate filter cake is fed to a flash dryer to produce a dry product which is discharged to the baghouse. The baghouse packs the dry iron precipitate into 1 m3 bulker bags which are then transported to the baghouse storage zone.

[0308] Example 3: Determination of carbon purity by thermogravimetric analysis Carbon purity was determined using thermogravimetric analysis (TGA) of purified graphite powder. TGA analysis of purified graphite was performed in two steps. In the first step, the temperature was increased to 100°C and held for 15 minutes to remove moisture, and then the temperature was ramped to 900°C in air to burn off any carbon. Weight loss occurred in two steps: removal of functional groups and subsequent weight loss due to carbon burnoff. The relative weight of the remaining material (corresponding to impurities) allows for the determination of carbon purity.

[0309] Example 4: Electrochemical purification of graphite Impure graphite (5.0 g) (e.g., as produced in Example 1) was packed into a dialysis bag (3.5 kDa MWCO) and a platinum wire, which served as a current collector, was inserted. The dialysis bag was sealed at both ends with plastic clips. The graphite in the dialysis bag was used as the working electrode (anode), and a graphite rod was used as the counter electrode (cathode).

[0310] The working and counter electrodes were immersed in 2 L of 0.1 M (NH4)2SO4 aqueous solution. A positive voltage (+10 V DC) was applied to the working electrode for 24 h. A photograph of the electrochemical setup is shown in Figure 5a, and a schematic diagram of the setup is shown in Figure 5b.

[0311] Impure graphite with an initial purity of 80.4% was used. The electrochemically purified graphite was washed multiple times (at least three times) with deionized water and centrifuged to remove any residual salts from the electrolyte solution. The dried powder was then used for characterization.

[0312] The carbon purity of the purified graphite was determined using thermogravimetric (TGA) analysis. The weight loss curve shown in Figure 6 indicates a weight loss of approximately 2% due to the moisture content of the electrochemical graphite powder. No significant weight loss was observed until the temperature reached approximately 500 °C, which may indicate a minimal degree of functionalization during the electrochemical process. The rapid weight loss at approximately 600 °C was attributed to the burnout of carbon, and the remaining weight was residual iron in oxide form. The carbon purity of this batch of electrochemically treated graphite was calculated to be 93.2% (by weight) after 24 hours of electrochemical treatment.

[0313] As discussed above, TGA analysis before and after electrochemical treatment shows that the carbon purity of the purified graphite after 24 hours of electrochemical treatment increases from 80.4% (by weight) for the impure untreated graphite to 93.2%.

[0314] The electrochemical treatment of yet another batch was carried out over a 48 hour period. In this batch, the electrolyte was replaced every 24 hours. The electrochemical treatment of the impure graphite over a 48 hour period is shown in FIG. 7. As shown in the photograph "Day 1; Start," the beaker initially contained a clear (NH)SO solution, which turned yellow after 2 hours ("Day 1; 2 hours").

[0315] At the end of the first day (Day 1; "After 24 hours"), the reaction batch containing the electrolyte became saturated with a red / orange sludge that began to flocculate and settle to the bottom of the beaker. Similar results were observed on Day 2, where the reaction bath again began to produce a flocculating red sludge.

[0316] As rationalized above with respect to the electrochemical reaction of aqueous ammonium sulfate, we believe that aqueous ferrous sulfate reacts with ammonium hydroxide in solution to produce insoluble ferrous hydroxide (Fe(OH)), a reddish-brown precipitate.

[0317] After 48 hours of electrochemical treatment, the graphite was analyzed by TGA to determine the purity of the graphite. The results are shown in Figure 8. The purity of the graphite increased from 80.2% for the impure untreated graphite to 93.2% on day 1 (Figure 6) and 96% on day 2 (Figure 8), demonstrating the effectiveness of the process of the present invention for purifying graphite.

[0318] Surprisingly, we have also found that the structure or morphology of the graphite is not affected by the process of the present invention. SEM micrographs of graphite before and after electrochemical treatment are shown in Figures 8a and 8b, respectively, and show the intact CNO and ANF structures after treatment.

[0319] Backscattered SEM micrographs were also taken of the treated graphite to examine the removal of iron from the graphite core; the results are shown in Figure 10. The image reveals many CMS and CNO morphological regions without iron cores, although some CNO still possesses residual iron (circled). Even after 48 hours of electrochemical treatment, most of the purified graphite structure remained intact, which was an unexpected result.

[0320] In another test batch, purified graphite was found to have an initial graphite purity of 90.2% and a purity of 99.6% after 48 hours of electrochemical treatment.

[0321] In a further test batch, the purified graphite was found to have a purity of 99.5% after 96 hours of electrochemical treatment, compared to an initial graphite purity of 85%, with the impurity being iron.

[0322] Further experimental data is shown in Table 4 below.

[0323] [Table 4]

[0324] The results shown in Table 4 above confirm that graphite purity of 99.5% can be achieved using the purification process of the present invention.

[0325] Example 5: Electrochemical purification using alternative electrolytes In Example 5, graphite was purified using the process of Example 1, using aqueous iron sulfate as the electrolyte.

[0326] The inventors surprisingly found that when using aqueous iron sulfate (FeSO), the insoluble iron species Fe(OH) does not contaminate the purified graphite, which could otherwise affect the purity of the graphite (or require costly treatments such as acid digestion after electrochemical treatment).

[0327] We observed an increase in graphite purity as a result of using iron sulfate electrolyte, and furthermore, no obvious precipitation of iron was observed in the graphite.

[0328] As shown in Figure 11, the use of iron sulfate as the electrolyte resulted in the formation of elemental iron dendrites on the cathode instead of the iron oxide that might otherwise be expected to form. The iron dendrites are then a valuable by-product that can be used, for example, as a catalyst in graphite formation processes such as the process described in Example 1.

[0329] Example 6: Electrochemical refining versus standard high temperature heat treatment To compare the purity of graphite material purified by the electrochemical process (ECP) of the present invention, graphite carbon material produced by catalytic decomposition of methane (CDM) using Fe ore as a catalyst was purified by standard high-temperature heat treatment and electrochemical process (ECP).

[0330] Material synthesis Specifically, graphitic carbon materials were synthesized in a fluidized-bed reactor operated with CH4 at 900 °C and 8 bar (g). Here, methane decomposes into graphite on the surface of an iron ore catalyst via "dusting" and hydrogen. The term "dusting" is an industry term used to describe the reaction that causes metallic materials (often ferrous materials) to break down into fragments and graphite in a carburizing environment. This effect begins when methane molecules (or other carbonaceous gases) adsorb and dissociate on the surface of the metal-containing catalyst, resulting in the diffusion of the resulting carbon to the surface of the bulk metal. When this outer layer becomes saturated with carbon, metal carbides form and then precipitate as graphitic carbon from the metal's grain boundaries. Over time, this creates intergranular pressures that separate the metal carbide particles from the parent bulk metal, disrupting the metal structure via "dusting."

[0331] The catalyst then dissociates, fragments into nanofragments, and becomes encapsulated within the carbon / graphite. The resulting graphitic carbon material encapsulating the Fe particles is hereafter referred to as "Carbon-O." Following standard thermal purification methods, Carbon-O was purified by high-temperature treatment up to 2800 °C in a vacuum furnace to remove the encapsulated Fe particles. The resulting material is designated "Carbon-T." For comparison, Carbon-O was also purified in an electrochemical cell (shown in Figure 5b) according to the electrochemical process (ECP) of the present invention. Here, Carbon-O was compressed into a carbon rod and subsequently used as the positive working electrode in the electrochemical cell. Platinum foil served as the negative counter electrode in a 0.1 M ammonium sulfate ((NH4)2SO4) electrolyte, and 10 VDC power was applied to the two electrodes. Charged ions in the electrolyte were intercalated between the graphene layers of the carbon material in the carbon rod, and the encapsulated Fe particles were slowly leached over a period of 20 hours. The resulting carbon material of the carbon rod is collected and designated "Carbon-E."

[0332] Besides the above three types of graphitic carbon materials, a commercial carbon conductive additive (Super P, Thermo Fisher) was also used as a reference.

[0333] The morphology of the carbon materials was examined by scanning electron microscopy (SEM, Zeiss, Gemini Ultra Plus). The average particle size of the carbon materials dispersed in water was analyzed using a particle size analyzer (Malvern Mastersizer 3000). Their surface area and pore structure were characterized by N2 physisorption using a pore size analyzer (Quantachrome Autosorb iQ). The density functional theory (DFT) method was used to calculate the pore size distribution from the N2 physisorption isotherm. Their chemical properties were characterized by Raman spectroscopy (Renishaw Raman inVia Reflex) with a 532 nm excitation laser. Their chemical composition was measured by heating the carbon materials in air flow at a temperature of 15 °C for 1 min. -1 The ash was investigated by thermogravimetric analysis (TGA) in a thermogravimetric analyzer (TA Instruments Q500) at a ramp rate of 25°C to 900°C. The elemental composition of the ash obtained after TGA was characterized by X-ray fluorescence spectroscopy (XRF) using a wavelength-dispersive XRF spectrometer (PANalytical AXIOS, PW2400) equipped with a 4-kW X-ray source.

[0334] Electrode fabrication and characterization First, MnO2 (electrolytic manganese dioxide - (EMD)) was homogenized in a planetary ball mill (Changsha Tianchuang Power Technology XQM-0.4) at 400 rpm for 5 h.

[0335] The EMD is one or more of α-, β-, γ-, δ-, or λ-MnO2.

[0336] In some embodiments, the EMD consists essentially of α-, β-, γ-, δ-, or λ-MnO 2 .

[0337] Good results were obtained when γ-MnO2 was used as the EMD.

[0338] Then, γ-MnO2, carbon conductive additive, and binder were mixed in a suitable solvent.

[0339] In some embodiments, the binder takes the form of a fluoropolymer binder that may be selected from the group consisting of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP), perfluoroalkoxyl polymer (PFA), and polyvinyl fluoride (PVF). In other embodiments, the binder may be selected from the group consisting of carboxymethyl cellulose (CMC), sodium alginate, starch, styrene-butadiene rubber (SBR), xanthan gum, polyvinyl chloride (PVC), polyacrylic acid (PAA), polyvinyl alcohol (PVA), polyethylene glycol (PEG), and polyamide-imide (PAI).

[0340] In some embodiments, the EMD, carbon conductive additive, and binder are mixed in a weight ratio of 4-9:2:1, preferably a weight ratio of 7:0.1-3:1, and more preferably a weight ratio of 4-9:0.1-3:0.1-3.

[0341] In one embodiment, the EMD, carbon conductive additive, and binder are mixed in a weight ratio of 7:2:1.

[0342] Good results were obtained using polyvinylidene fluoride (PVDF) as a binder, mixing γ-MnO2, carbon conductive additive and polyvinylidene fluoride (PVDF) binder in N-methyl-2-pyrrolidone (NMP) at a weight ratio of 7:2:1.

[0343] Four carbon materials (Super P, Carbon-O, Carbon-T, and Carbon-E) were separately used as conductive additives. The resulting slurry was then cast onto a conductive metal foil using a doctor blade method to form an at least partial coating on the conductive metal foil having a thickness ranging from about 1 micron to about 25 microns. For example, the coating thickness was about 1, 2, 3, 4, 5, 10, 12.5, 15, 17.5, 20, 22.5, 25, 27.5, or 30 microns. 2 / g and may be about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24 or about 25 microns.

[0344] In some embodiments, the resulting slurry is preferably cast onto a conductive metal foil to form a coating surrounding the conductive metal foil with a thickness ranging from about 5 microns to about 20 microns, more preferably from about 7 microns to about 15 microns.

[0345] Suitable conductive metal foils may be selected from the following group of conductive metal foils consisting of titanium, copper, zinc, aluminum, iron, or any mixture thereof.

[0346] Good results were obtained when the slurry was cast onto Ti foil at a thickness of about 10 μm and then dried in a vacuum oven at 80° C. for 12 hours.

[0347] The mass loading of the active electrode material on the Ti foil is approximately 2.5 mg cm -2 Finally, the Ti foil coated with the electrode material slurry was punched into a 1.1 cm diameter hole using a punching machine. 2 was cut into small pieces.

[0348] The in-plane electrical conductivity of EMD cathodes fabricated using different carbon materials was examined using a four-point probe sheet resistance meter (Guardian SRM-232). -1 ) is σ=1 / R S t, where RS where (Ω / sq) is the sheet resistance and t is the thickness of the electrode material. The electrolyte absorption capacity of the carbon conductive additive was measured by immersing a carbon electrode (without EMD) made with carbon material (90 wt.%) and PVDF (10 wt.%) in an equal volume of 1 M zinc sulfate (ZnSO4) solution and recording the weight gain as a function of time.

[0349] Zn-C battery fabrication and characterization The prepared EMD cathode and Zn metal foil (1.1 cm) as the anode. 2 Coin cells (2032 type) were assembled using 1M ZnSO4 solution as the electrolyte, and their electrochemical performance was evaluated. A CHI 760D electrochemical workstation was used to perform constant current charge / discharge (GCD) in the voltage range of 1.5 to 0.7 V, and 10 6 Electrochemical impedance spectroscopy (EIS) measurements were collected in the frequency range between 0.008 Hz and 50 mAg. The specific capacity of the battery was calculated based on the mass of EMD in the cathode. -1 Constant Current Intermittent Titration Technique (GITT) tests were performed on the assembled batteries using a battery testing system (LANHE) with a series of 120-second constant current discharge pulses at 1000 kJ / s followed by a 4-hour rest period. The battery testing system was also used to test the long-term stability of the batteries by continuously recording the open circuit voltage (OCV) over a 1-month rest period. All electrochemical tests were performed at room temperature. Example 7: Summary of ECP results [Table 5] [Table 6] [Table 7]

[0350] Example 8: Further study of the ECP process Further studies were conducted to investigate various operating conditions that may affect the ECP process results. This study was carried out for 2 days using 20 g of graphite (66.54% purity, original sample), 0.1 M (unless otherwise stated) (NH4)2SO4 as the electrolyte, a black cloth filter bag, two Pt-coated Ti electrodes, and 10 V (unless otherwise stated).

[0351] Electrolyte stirring For the ECP process with agitated electrolyte (Study 1a), the graphite purity was 96.2% compared to the process without agitation (Study 1b).

[0352] Bag compression In the ECP process where the black cloth filter bags were compressed, the graphite purity was 96.2% compared to the process without compression (Study 2).

[0353] · Voltage For the ECP process operating at 7 V (Study 3a), the graphite purity was 94.2%. For processes operating at 10 V and 20 V (Study 3b), the purities were 96.2% and 98.8%, respectively.

[0354] · Electrolyte concentration For a 0.1 M concentration of electrolyte, the graphite purity was 96.2%. When operating at 0.5 M (Study 4a) and 1.0 M (Study 4b), the purity was 99.13% and 99.26%, respectively.

[0355] · Distance between electrodes When the electrode distance was 5 cm (Study 5), the graphite purity was 99.13%. When operating at 10 cm, the purity was also 99.13%.

[0356] Electrode size When the electrode size was 1.5 cm × 10 cm × 25 μm, the graphite purity was 99.13%. When the electrode size was 2.5 cm × 10 cm × 25 μm (Study 6), the purity was 99.27%.

[0357] Response duration Samples were collected at regular time intervals and analyzed, and the results are shown below in Table 6. In this study, it was found that for this particular original sample, the majority of the purification occurred in the first 6 hours. [Table 8]

[0358] Effect of operating conditions on graphite properties The morphology of the sample was examined by scanning electron microscopy (SEM, Zeiss, HD). The original carbon material (purity 66.54%) was a mixture of various morphologies, including carbon nano-onions (CNO), carbon nanotubes (CNT), and microcarbon shells (MCS), which are micrometer-sized structures with numerous surface irregularities, as shown in Figure 16. The bright spots observed in the FESEM image are Fe particles mostly coated with graphitic carbon resulting from the catalytic decomposition of methane.

[0359] The morphology of the samples obtained from the above study was studied by FESEM. As shown in Figure 17, the resulting morphology does not show any significant changes compared to the original sample, except that the bright spots representing the Fe particles are now sparser.

[0360] The average particle size of the carbon material (5 mg / mL) dispersed in ethanol was analyzed using a particle size analyzer (Malvern Mastersizer 3000) according to the wet PSD instructions. As shown in Table 7, the average particle size distribution was relatively smaller for all of the ECP-treated samples compared to the original sample. [Table 9]

[0361] The surface area and pore structure of the original and ECP-treated samples, which showed significant changes in final purity levels due to variations in operating parameters, were characterized by N2 physisorption using a pore size analyzer (Quantachrome Autosorb iQ). Density functional theory (DFT) methods were used to calculate the pore size distributions from the N2 physisorption isotherms. The results for all tested samples are shown in Figures 18a and 18b. Their BET-specific surface areas varied from 15.47 to 34 m2 g-1 according to the following order: Original < Study 6 < Study 4b < Study 3b < Study 1b. Their pore size distributions, determined by DFT methods, range from micropores (<2 nm) to macropores (>10 nm), as shown in Figure 18. It is noteworthy that the surface area increased after electrochemical purification due to the expansion and exfoliation of the graphite layers.

[0362] Finally, the effect of ECP treatment on the structural changes of graphite was investigated using X-ray diffraction (XRD) patterns (Pananalytical Flat Plate Powder XRD) using a diffractometer under Cu-Kα radiation. The XRD pattern of the original sample, along with multiple diffraction peaks, is shown in Figure 19a. The most intense peaks at 2θ = 26.38° and 2θ = 44.72° are attributed to graphitic carbon and metallic iron. In addition, several other diffraction peaks attributed to metallic Fe and Fe3C were also observed. The most intense Fe peaks are attributed to metallic Fe (2θ = 44.67, 65.02, and 82.33°, according to JCPDS No. 06-0696) and Fe3C (2θ = 37.64, 37.76, 42.89, 44.57, and 45.00°, according to JCPDS No. 89-7271). The XRD patterns of the ECP-treated samples shown in Figure 19c and d indicate that Fe species have been largely removed from the graphitic structure.

[0363] Results and Discussion Carbon material properties The SEM image of Figure 20 shows the morphology of four types of carbon materials (Super P, Carbon-O, Carbon-T, and Carbon-E). Super P, unlike the other three graphite carbon materials synthesized by CDM, exhibits a powdery and particulate morphology with a nanometer-scale particle size. Those carbon materials mainly consist of micrometer-sized块状 structures with numerous irregularities on the surface. Carbon-O shows a coarser surface topography, while Carbon-T and Carbon-E have a relatively smooth surface formed by irregularly shaped particles composed of carbon flakes. Their average particle sizes were analyzed using a particle size analyzer. As shown in Figure 21, when dispersed in an aqueous solution, all of Super P, Carbon-O, and Carbon-T have a similar median diameter (D 50 ) in the range of 9.1 - 12.4 μm. In comparison, Carbon-E has a small size of about 1.9 μm.

[0364] The specific surface area and pore structure of the carbon materials were characterized by N2 physical adsorption. Figure 22a shows their N2 physical adsorption isotherms. Their BET-specific surface areas vary from 19 to 37 m 2 g -1 in the order of Carbon-T < Carbon-O < Carbon-E. Super P has a much larger surface area of 78 m 2 g -1 . Their pore size distributions determined by the DFT method are shown in Figure 22b. Super P has a maximum pore volume of 1.83 cm 3 g -1 and an average pore size of 36 nm, indicating its mesoporous nature. Carbon-O and Carbon-E show a wide pore size distribution ranging from micropores to macropores. The pore volumes and average pore sizes of Carbon-O and Carbon-E are 0.13 cm 3 g -1 , 3.8 nm, and 0.15 cm 3 g<0, -1, 2.9 nm, indicating that the electrochemical purification process does not significantly alter the porous structure of Carbon-O. In contrast, Carbon-T has a pore size distribution centered around 30.1 nm and a pore size distribution of 0.30 cm. 3 g -1 The disappearance of small pores and the increase in pore volume in Carbon-T may be related to the complete removal of metal residues trapped within the carbon and the restructuring and closure of small pores at high temperatures.

[0365] The chemical structure of the carbon materials was first analyzed by Raman spectroscopy. Figure 22c shows their Raman spectra, which have three typical carbon material features: the G band, which corresponds to the zone-center vibration of the carbon atoms within the graphene plane; the D band, which is related to the disorder within the graphite lattice; and the G' band, which is related to the number of graphene layers and their stacking order. Super P exhibits only the D and G bands, suggesting the absence of long-range graphitic structure. The intensity ratio of the D and G bands (I D / I G ) can be correlated with defects, structural vacancies, and surface functional groups in carbon materials. D / I G The ρ is 1.18, which is higher than 0.73 for Carbon-O, 0.84 for Carbon-E, and 0.29 for Carbon-T. These results indicate that Carbon-T has the lowest level of defects due to its high-temperature processing conditions. In contrast, Carbon-E has a relatively high concentration of defects due to the exfoliation of the graphene layers during purification. Super-P has the most defective structure.

[0366] Their chemical structures and metal residues were further examined by TGA. Figure 22d and its inset show the weight loss profiles in air as the temperature increased from 25 °C to 900 °C (for Carbon-T, from 25 °C to 1040 °C due to its higher thermal stability). The differential thermogravimetric (DT) profiles are shown in Figure 23. The main weight loss of Carbon-T occurred at the highest temperature of 882 °C, suggesting the highest graphite level. The main weight loss temperature of Super P, 776 °C, is also higher than that of Carbon-E and Carbon-O. Carbon-O has the lowest main weight loss temperature of 632 °C, which is attributed to the oxidative decomposition of carbon catalyzed by Fe residues. Furthermore, Carbon-E exhibits some weight loss starting at 48 °C, resulting from volatile components formed during electrochemical refining. Carbon-T has the lowest ash content of 0.18 wt.% and the highest carbon purity of 99.82 wt.%. Carbon-E and Super P also have high purity of 99.59 wt.% and 99.47 wt.%, respectively. Carbon-O has the highest ash content of 31.10 wt.%. XRF was used to analyze the chemical composition of the ash residue obtained after TGA.

[0367] As shown in Table 8, Fe2O3 accounts for 95.32 wt.% of the ash, which is formed by oxidation of Fe residues encapsulated within the carbon material. The purity of Carbon-O is estimated to be 78.25 wt.%. [Table 10]

[0368] Characteristics of the produced electrodes EMD electrodes were fabricated using different carbon materials as conductive additives in the same mass ratio. The electrical conductivity of the fabricated electrodes can be affected by several factors, such as the graphitic structure of the carbon additive as well as its particle size, surface area, and porosity.

[0369] The inventors have found that the in-plane electrical conductivity of EMD electrodes fabricated using these materials is approximately 70 Sm -1 ~approx. 100Sm -1 For example, the in-plane electrical conductivity of these particular EMD electrodes has been observed to be within the range of about 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99 or about 100 Sm -1 In some embodiments, the in-plane electrical conductivity of these particular EMD electrodes is preferably about 80 S m -1 ~approx. 95mm -1 More preferably, it is in the range of about 90Sm -1 is.

[0370] For example, as shown in Table 9, the in-plane electrical conductivity of the EMD electrode fabricated using Super P was 72 Sm -1 In comparison, the EMD electrodes fabricated using two purified carbon materials, Carbon-T and Carbon-E, had the lowest Sm values ​​of 98 and 90 Sm, respectively. -1 The higher electrical conductivity correlates with its higher graphitic properties, as shown by the Raman results. The difference in pore size between Carbon-T and Carbon-E does not appear to have a significant effect on the electrical conductivity. The larger surface area of ​​Super P also does not have a beneficial effect on the electrical conductivity of the electrode. The electrode fabricated using Carbon-O exhibits a 143Sm -1 It has the highest electrical conductivity of I D / I G The higher ratio may be related to its significant proportion of Fe residues, given that the specific surface area and average pore size are similar to Carbon-E. [Table 11]

[0371] Another essential function of the carbon conductive additive is to absorb and retain the electrolyte to maintain a stable solid-liquid interface within the electrode. However, an extremely high electrolyte capacity can consume more electrolyte and increase the manufacturing cost of the battery. The electrolyte absorption capacity is affected by the pore volume, pore size, and surface area of the carbon additive. Figure 24 shows the electrolyte uptake (in mg of electrolyte per mg of carbon) in 5 minutes by different types of carbon materials when a carbon electrode is immersed in a 1M ZnSO4 solution. Due to the substantially larger specific surface area and pore volume of Super P, the electrolyte renewal is faster, and after 5 minutes, the highest absorption capacity of 10.94, which is about 6 times that of Carbon-O's 1.84, was obtained. The electrolyte absorption capacities of 2.14 for Carbon-T and 4.20 for Carbon-E are both higher than that of Carbon-O.

[0372] Characteristics of the assembled Zn / C battery Next, Zn / C batteries were assembled using EMD cathodes and Zn metal anodes manufactured with different carbon conductive additives in a 1M ZnSO4 aqueous electrolyte. Figures 25a - d show their constant current discharge curves at voltage windows of 1.5 - 0.7V at current densities of 1.0, 0.5, 0.1, and 0.05 Ag -1 respectively. All discharge curves are characteristic of the typical discharge behavior of Zn-C batteries, reaching a flat discharge plateau from the ohmic voltage drop (IR drop) at the start of discharge and then decreasing in voltage to the cut-off voltage. At high current densities of 1.0 and 0.5 Ag -1 , the Zn-C cells containing the graphite carbon material synthesized by CDM exhibit significantly higher specific discharge capacities than those containing Super P. The Carbon-T cell provides a specific capacity 1.4 times that of the Super P cell at 1.0 Ag -1 . In comparison, at a lower current density of 0.1 Ag -1 , only slight differences were observed. The specific capacities vary from 99 to 104 mAhg in the order of Carbon-O cell < Carbon-T cell < Carbon-E cell < Super P cell -1 . At 0.05 Ag -1At the lowest current density, the specific capacity of the Carbon E cell is 0.05Ag -1 When measured between 1.5V and 0.7V at a current density of -1 ~About 200mAhg -1 Between 100 and 1500, preferably about 70mAhg -1 ~about 120mAhg -1 and more preferably in the range of about 109 mAhg -1 This result is 124mAhg for the Super P cell. -1 The specific capacities of Carbon-O and Carbon-T (122 and 114 mAhg, respectively) are comparable to those of -1 (measured as

[0373] Figure 25e compares their specific capacities at different discharge current densities. All batteries were tested at 0.05 to 1.0 Ag -1 The cells experience a decrease in capacity with increasing discharge current density up to 1000 kJ / s, with the Super P cell showing the most significant drop. Figure 25f shows the Nyquist plot of the EIS spectra of the Zn-C cells. The intercept of the impedance curve with the real axis indicates the ohmic resistance.

[0374] As shown in the inset of Figure 25f, the Super P cell exhibits a larger ohmic resistance, consistent with the lower measured in-plane electrical conductivity of the EMD electrode. Only slight differences were observed in the ohmic resistance of the Carbon-T, Carbon-E, and Carbon-O cells. Furthermore, based on the semicircles in the high-frequency region, the Carbon-T, Carbon-E, and Carbon-O cells have much lower charge transfer resistance than the Super P cell. Previous studies have reported that due to the aggregation of Super P particles, the carbon conductive additive network may not completely cover all EMD particles. In contrast, the other three types of carbon particles appear to fill the gaps between EMD particles more efficiently. The charge transfer resistance of the Carbon-O cell is close to that of the Carbon-T and Carbon-E cells, suggesting that despite the high in-plane conductivity of the EMD electrode fabricated with Carbon-O, the Fe residue in Carbon-O plays a negative role in promoting electron transfer at the electrode / electrolyte interface.

[0375] Overall, Zn-C batteries fabricated with CDM-synthesized graphitic carbon materials perform better than those fabricated with Super P at high discharge current densities and comparable at low discharge current densities. The improved performance at high discharge rates is associated with the higher electrical conductivity of the CDM-synthesized carbon materials and the effective electronic network thereby formed within the battery.

[0376] Furthermore, the GITT technique was used to investigate the voltage response of the Zn-C cells under intermittent operating conditions, which are more relevant to practical operating conditions. As shown in Figure 26a, all cells were charged at 0.05Ag -1The cells were discharged at 1000 kJ / s for 120 seconds, followed by a 4-hour rest period, and this test cycle was repeated for 30 segments. Figure 26b shows an enlarged region of the GITT fragment during the third test cycle, demonstrating the voltage relaxation process during the rest period. The instantaneous voltage jump (IR drop) correlates with ohmic resistance and charge transfer resistance. The subsequent gradual voltage change is associated with ion diffusion. The Carbon-T and Carbon-E cells exhibited smaller IR drops of 26 mV and 27 mV, respectively, indicating lower internal resistance. The total voltage changes of the Super P, Carbon-O, Carbon-T, and Carbon-E cells were 105, 94, 82, and 91 mV, respectively, showing a similar trend to the IR drops. The smallest voltage change for the Carbon-T cell can be attributed to its lowest resistance and better ion diffusion. The internal resistance of all cells increased with the test time, which can be calculated by Ohm's law: R = V / I. where V (V) is the maximum voltage change in one segment and I (A) is the discharge current.

[0377] As shown in FIG. 26c, throughout the GITT segment, the Super P cell has the highest cell resistance and the fastest rate of increase, and the Carbon-T cell has the lowest cell resistance and the slowest rate of increase.

[0378] Figure 26d compares the long-term stability over one month of Zn-C batteries fabricated with different carbon conductive additives. The Carbon-O cell shows the largest OCV drop of 0.037 V, which is due to Fe residue in the Carbon-O, which can cause self-discharge or secondary reactions. In contrast, the Carbon-T and Carbon-E cells show negligible OCV drops of 0.001 and 0.020 V, respectively, which are superior to the 0.014 V of the Super-P cell. These stability improvements indicate that both purification methods successfully removed the Fe residue, avoiding its adverse effect on the long-term performance of the batteries. After the stability test, all Zn-C cells were recharged with 0.1 Ag of 0.1 Ag. -1The discharge characteristics were evaluated after a long-term storage period. Figure 27 shows the discharge curve of the Zn-C battery, which was similar, with a specific capacity of approximately 95 mAhg when discharged to 0.7 V. -1 This indicates that

[0379] conclusion Graphitic carbon materials (Carbon-O) were synthesized by CDM using Fe ore as a catalyst as a by-product of H2. They were purified by standard high-temperature heat treatment at 2800 °C (Carbon-T) and an alternative electrochemical method (Carbon-E), increasing the carbon purity from 78.25 to 99.82 and 99.59 wt.%, respectively. They were evaluated as conductive carbon additives for Zn-C batteries. MnO2 cathodes fabricated using Carbon-T or Carbon-E at a mass ratio of 7:2 exhibited 98 and 90 Scm -1 The carbon electrodes showed electrical conductivities of 2.14 and 4.20 mg / cm², respectively. -1 The Zn-C battery assembled with Carbon-T or Carbon-E has an electrolyte (1M ZnSO4) absorption capacity of 0.05Ag -1 114 and 109 mAhg, respectively -1 This is comparable to the commercially available carbon conductive additive (Super P). Importantly, these materials are able to achieve current densities of 0.05 to 1.0 Ag due to the high electrical conductivity resulting from the graphite structure. -1 The results show better rate performance when the concentration of carbon dioxide is increased. They also perform well under intermittent operating conditions and in long-term stability tests, as the efficient removal of Fe residues prevents self-discharge behavior. There is no significant difference between Carbon-T and Carbon-E, indicating that both purification methods are efficient. Graphitic carbon materials purified from CDM are promising as efficient carbon conductive additives for batteries, transforming solid waste from CDM into high-value-added products and enhancing the economic viability of CDM-based H2 production processes.

[0380] Important Features of the Invention The present investigation has yielded several important findings, which can be summarized as follows:

[0381] The ECP process is effective for graphite slurries; graphite slurries have lower electrical conductivity than packed graphite; the reaction rate is correspondingly slower; the distance between the electrodes in an ECP process affects the reaction rate and is a major design consideration; an increase in voltage increases the reaction rate approximately proportionally.

[0382] Regarding the feasibility of separating the iron by-product: the iron by-product is an iron salt complex, such as ammonium jarosite; the iron by-product cannot be easily separated from the graphite by physical separation techniques such as centrifugation; the iron by-product can be dissolved in H2SO4 as an alternative washing step.

[0383] Regarding the electrolyte: H2SO4 and FeSO4 were tested as alternative electrolytes; the performance of both alternative electrolytes was comparable to that of (NH4)2SO4; all electrolytes were able to purify graphite from a pilot plant with an initial purity of 80% to over 93%; H2SO4 does not produce observable solid by-products but produces significant amounts of H2 and O2 at the electrode; using FeSO4 as the electrolyte allows iron from both the electrolyte and the graphite to be recovered at the cathode.

[0384] Finally, a Zn / C battery fabricated using a negative electrode comprising a metal foil substrate coated with purified graphite material produced by the ECP process showed a 0.05Ag -1 When measured between 1.5V and 0.7V at a current density of at least about 109mAhg -1 The specific discharge capacity was

[0385] Those skilled in the art will appreciate that the invention described above is susceptible to variations and modifications other than those specifically described, and it is to be understood that the invention includes all such variations and modifications that fall within its spirit and scope.

[0386] Future patent applications may be filed in Australia or overseas based on or claiming priority to this application. It should be understood that the provisional claims below are provided by way of example only and are not intended to limit the scope of what may be claimed in any such future application. Features may be added to or omitted from the provisional claims at a later date in order to further define or redefine the invention or inventions.

Claims

1. 1. A method for purifying a graphite material, comprising: electrochemically treating a crude graphite material containing impurities selected from metals, metal oxides, and combinations thereof; Use of a prescribed electrolyte; Over a specified period of time; spanning a predetermined voltage range; Over a predetermined temperature range; Using a predetermined anode composition; Using a Predetermined Cathode Composition whereby a portion of said impurities are removed as a result of said electrochemical treatment to provide a purified graphite material.

2. 10. The method of claim 1, further comprising a predetermined semi-permeable membrane for protecting said cathode from shorting when in contact with said graphite material.

3. 3. The method of claim 1 or 2, wherein the purified graphite material has substantially the same morphology as the crude graphite material, the graphite material having a morphology selected from graphite fibers (including carbon nanotubes), carbon nano-onions, carbon microspheres, and graphene.

4. The method of any one of claims 1 to 3, wherein the impurities are selected from metals, metal oxides, and combinations thereof.

5. 5. The method of claim 4, wherein the impurities are selected from iron, elemental iron, iron oxides, iron-carbon species such as ferrite, austenite, or cementite, and combinations thereof.

6. The method of any one of claims 1 to 5, wherein the electrolyte is ammonium sulfate, iron sulfate, nitric acid, sulfuric acid, or a mixture thereof.

7. 7. The method of claim 5 or 6, wherein the iron impurities deposit on the cathode as elemental iron, precipitate as iron hydroxide or iron complexes, or remain in solution.

8. The method according to any one of claims 1 to 7, wherein the voltage range is between about 1V and 300V, preferably between about 5V and 300V.

9. The method according to any one of claims 1 to 8, wherein the period is between about 2 hours and about 2 weeks, preferably between about 2 hours and 96 hours.

10. The method of any one of claims 1 to 9, wherein the temperature range is between about 5°C and about 100°C.

11. 11. The method of any one of claims 1 to 10, wherein the cathode comprises one or more of a metal, a metal alloy plate, platinum, or platinum-coated titanium, and the anode comprises graphite, lead, a lead alloy, platinum, platinum-coated titanium, and combinations thereof.

12. 12. The method of claim 11, further comprising the use of a permeable membrane coating at least a portion of the anode, the cathode, or both, wherein the permeable membrane is a neutrally charged permeable membrane, an anion exchange membrane, or a cation exchange membrane, and wherein the permeable membrane has a molecular weight cut-off (MWCO) of less than about 1 million Da, preferably between about 10 kDa and about 0.5 kDa.

13. The permeable membrane has a flow rate of 0.1 to 100 L / min / dm at 200 Pa. ２ The method of claim 12, having an air permeability of between 0.01 and 0.

01.

14. 14. The method of any one of claims 1 to 13, wherein the purified graphite material has a purity of greater than about 95% w / w, preferably greater than about 99% w / w, more preferably greater than about 99.5% w / w, even more preferably greater than about 99.95% w / w.

15. The method of any one of claims 1 to 14, wherein the crude graphite material is slurried prior to the electrochemical treatment method.

16. The method of any one of claims 1 to 15, wherein the rate of the purification reaction is proportional to the applied voltage.

17. A purified graphite material obtained or obtainable from the method according to any one of claims 1 to 16.

18. 1. A negative electrode material comprising a coating on a substrate, the coating comprising MnO ２ 20. A negative electrode material comprising: (electrolytic manganese dioxide (EMD)), a carbon conductive additive in the form of the purified graphite material of claim 17, and a binder.

19. The EMD may be α-, β-, γ-, δ-, or λ-MnO ２ 19. The electrode of claim 18, wherein the electrode is one or more of:

20. 20. The electrode of claim 18 or 19, wherein the EMD, the carbon conductive additive, and the binder are mixed in a weight ratio of 4-9:2:

1.

21. 21. The electrode of any one of claims 18 to 20, wherein the binder is selected from the group consisting of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP), perfluoroalkoxyl polymer (PFA), polyvinyl fluoride (PVF), carboxymethyl cellulose (CMC), sodium alginate, starch, styrene-butadiene rubber (SBR), xanthan gum, polyvinyl chloride (PVC), polyacrylic acid (PAA), polyvinyl alcohol (PVA), polyethylene glycol (PEG), and polyamideimide (PAI).

22. 22. The electrode of any one of claims 18 to 21, wherein the substrate comprises a metal foil made of a conductive foil selected from the group consisting of copper, zinc, aluminum, iron, or any mixture thereof.

23. 23. The electrode of any one of claims 18 to 22, wherein the coating at least partially surrounds the substrate, and the coating has a thickness in the range of about 1 micron to about 25 microns.

24. The negative electrode has a capacitance of about 70 Sm －１ ~ approx. 100 Sm －１ 24. The electrode according to claim 18, having an electrical conductivity in the range of

25. A positive electrode and a negative electrode; an electrolyte in contact with the positive electrode and the negative electrode; the negative electrode comprises a coating on a substrate, the coating being MnO ２ 20. A battery comprising: (electrolytic manganese dioxide (EMD)), a carbon conductive additive in the form of the purified graphite material of claim 17, and a binder.

26. The EMD may be α-, β-, γ-, δ-, or λ-MnO ２ 26. The battery of claim 25, wherein the

27. 27. The battery of claim 25 or 26, wherein the EMD, the carbon conductive additive, and the binder are mixed in a weight ratio of 4-9:2:

1.

28. 28. The battery of any one of claims 25 to 27, wherein the binder is selected from the group consisting of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP), perfluoroalkoxyl polymer (PFA), polyvinyl fluoride (PVF), carboxymethyl cellulose (CMC), sodium alginate, starch, styrene-butadiene rubber (SBR), xanthan gum, polyvinyl chloride (PVC), polyacrylic acid (PAA), polyvinyl alcohol (PVA), polyethylene glycol (PEG), and polyamideimide (PAI).

29. 29. The battery of any one of claims 25 to 28, wherein the substrate comprises a metal foil made of a conductive metal selected from the group consisting of copper, zinc, aluminum, iron, or any mixture thereof.

30. 30. The battery of any one of claims 25 to 29, wherein the coating at least partially surrounds the substrate, and the coating has a thickness in the range of about 1 micron to about 25 microns.

31. The negative electrode has a capacitance of about 70 Sm －１ ~ approx. 100 Sm －１ The battery according to any one of claims 25 to 30, having an electrical conductivity in the range of

32. 32. The battery of any one of claims 25 to 31, wherein the electrolyte is an aqueous electrolyte present at a concentration in the range of about 0.01M to about 10.0M.

33. The electrolyte may be ammonium sulfate, sodium sulfate, magnesium sulfate, iron sulfate, copper sulfate, zinc sulfate (ZnSO ４ ), zinc chloride (ZnCl ２ ), zinc trifluoromethylsulfonate (Zn(CF ３ SO ３ ) ２ ), cadmium nitrate, cobalt nitrate, sodium nitrate, sodium chloride, nickel chloride, potassium chloride, ammonium chloride (NH ４ 33. The battery of any one of claims 25 to 32, wherein the aqueous electrolyte is selected from the group consisting of potassium chloride, potassium iodide, potassium chloride, calcium chloride, sulfuric acid, and combinations thereof.

34. The electrolyte is an ionic liquid comprising a cation selected from the group consisting of 1-alkyl-3-methyl-imidazolium, N-alkyl-pyridinium, tetraalkyl-ammonium, tetraalkyl-phosphonium, 1-ethyl-3-methyl-1H-imidazolium, 1-butyl-3-methyl-1H-imidazolium, 1-butylpyridinium, and combinations thereof, and the alkyl group is selected from the group consisting of C ２ ~C １２ The battery of any one of claims 25 to 33, wherein the alkyl group is selected from the group consisting of alkyl.

35. The electrolyte is ZnSO present at a concentration ranging from about 0.01 M to about 10 M. ４ The battery according to any one of claims 25 to 34, wherein

36. 36. The battery of any one of claims 25 to 35, wherein the positive electrode is a zinc metal electrode.

37. The negative electrode is 0.05Ag －１ When measured between 1.5V and 0.7V at a current density of about 50mAhg －１ ~About 200mAhg －１ 37. The battery of claim 25, wherein the specific discharge capacity is in the range between:

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